I have followed below instrustions 

• Remove unused plugins from your installation
• Remove deprecated plugins from your installation
• Remove plugins with security issues from your installation

Here are details from the script
Jenkins: 2.277.3
OS: Windows Server 2012 - 6.2
—
ace-editor:1.1
ant:1.11
antisamy-markup-formatter:1.6
apache-httpcomponents-client-4-api:4.5.13-1.0
applitools-eyes:1.13
authentication-tokens:1.4
backup:1.6.1
bitbucket-oauth:0.10
bitbucket:1.1.27
block-build-final-project:1.0
blueocean-autofavorite:1.2.4
blueocean-bitbucket-pipeline:1.24.6
blueocean-commons:1.24.6
blueocean-config:1.24.6
blueocean-core-js:1.24.6
blueocean-dashboard:1.24.6
blueocean-display-url:2.4.1
blueocean-events:1.24.6
blueocean-git-pipeline:1.24.6
blueocean-github-pipeline:1.24.6
blueocean-i18n:1.24.6
blueocean-jira:1.24.6
blueocean-jwt:1.24.6
blueocean-personalization:1.24.6
blueocean-pipeline-api-impl:1.24.6
blueocean-pipeline-editor:1.24.6
blueocean-pipeline-scm-api:1.24.6
blueocean-rest-impl:1.24.6
blueocean-rest:1.24.6
blueocean-web:1.24.6
blueocean:1.24.6
bootstrap4-api:4.6.0-3
bouncycastle-api:2.20
branch-api:2.6.3
build-blocker-plugin:1.7.7
build-timeout:1.20
categorized-view:1.10
checks-api:1.7.0
cloudbees-bitbucket-branch-source:2.9.8
cloudbees-folder:6.15
command-launcher:1.5
conditional-buildstep:1.4.1
copyartifact:1.46
credentials-binding:1.24
credentials:2.3.18
cucumber-reports:5.5.0
cucumber-testresult-plugin:0.10.1
cucumber-trends-report:1.3
CucumberReportMailer:1.0-SNAPSHOT (private-03/03/2020 20:04-lagisesu)
discard-old-build:1.05
display-url-api:2.3.4
docker-commons:1.17
docker-workflow:1.26
durable-task:1.35
echarts-api:5.1.0-2
email-ext:2.82
external-monitor-job:1.7
favorite:2.3.3
font-awesome-api:5.15.2-2
git-client:3.7.1
git-server:1.9
git:4.7.1
gitbucket:0.8
github-api:1.123
github-branch-source:2.10.2
github-oauth:0.33
github:1.33.1
global-build-stats:1.5
gradle:1.36
groovy:2.3
handlebars:3.0.8
handy-uri-templates-2-api:2.1.8-1.0
hp-application-automation-tools-plugin:6.8
htmlpublisher:1.25
jackson2-api:2.12.3
javadoc:1.6
jdk-tool:1.5
jenkins-design-language:1.24.6
jira:3.2.1
jjwt-api:0.11.2-9.c8b45b8bb173
job-import-plugin:3.4
jobConfigHistory:2.27
join:1.21
jquery-detached:1.2.1
jquery-ui:1.0.2
jquery:1.12.4-1
jquery3-api:3.6.0-1
jsch:0.1.55.2
junit:1.49
ldap:2.6
lockable-resources:2.10
mail-watcher-plugin:1.16
mailer:1.34
mapdb-api:1.0.9.0
matrix-auth:2.6.6
matrix-project:1.18
maven-plugin:3.10
mercurial:2.14
metrics:4.0.2.7
mock-security-realm:1.5
momentjs:1.1.1
monitoring:1.87.0
naginator:1.18.1
notification:1.14
oic-auth:1.8
okhttp-api:3.14.9
ownership:0.13.0
pam-auth:1.6
parameterized-trigger:2.40
pipeline-build-step:2.13
pipeline-github-lib:1.0
pipeline-graph-analysis:1.10
pipeline-input-step:2.12
pipeline-milestone-step:1.3.2
pipeline-model-api:1.8.4
pipeline-model-declarative-agent:1.1.1
pipeline-model-definition:1.8.4
pipeline-model-extensions:1.8.4
pipeline-rest-api:2.19
pipeline-stage-step:2.5
pipeline-stage-tags-metadata:1.8.4
pipeline-stage-view:2.19
plain-credentials:1.7
plugin-util-api:2.1.0
poll-mailbox-trigger-plugin:1.026
popper-api:1.16.1-2
postbuild-task:1.9
pubsub-light:1.13
purge-job-history:1.6
queue-cleanup:1.4
repository:1.3
resource-disposer:0.15
role-strategy:3.1.1
run-condition:1.5
scm-api:2.6.4
script-security:1.76
snakeyaml-api:1.27.0
sse-gateway:1.24
ssh-credentials:1.18.1
ssh-slaves:1.30.2
structs:1.22
subversion:2.14.0
support-core:2.73
testng-plugin:1.15
thinBackup:1.10
timestamper:1.12
token-macro:2.15
trilead-api:1.0.13
variant:1.4
view-job-filters:2.3
windows-slaves:1.7
workflow-aggregator:2.6
workflow-api:2.42
workflow-basic-steps:2.23
workflow-cps-global-lib:2.18
workflow-cps:2.90
workflow-durable-task-step:2.38
workflow-job:2.40
workflow-multibranch:2.23
workflow-scm-step:2.12
workflow-step-api:2.23
workflow-support:3.8
ws-cleanup:0.39
cucumber-perf:2.0.9
cucumber-living-documentation:3.2

Also seeing this errors in the console log

See my description in https://issues.jenkins.io/browse/JENKINS-65304?focusedCommentId=408437&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-408437 . I'm unable to duplicate the problem you're describing.

More details will be needed, like the details of the specific job that won't save or if all defined jobs won't save or only one or if the problem persists when you remove the CucumberReportMailer:1.0-SNAPSHOT plugin

Hello markewaite, thank you for the analysis. 

please find the updated information, I've also uninstalled the custom plugin.
Jenkins: 2.277.3
OS: Windows 10 - 10.0
—
ace-editor:1.1
ant:1.11
antisamy-markup-formatter:2.1
apache-httpcomponents-client-4-api:4.5.13-1.0
applitools-eyes:1.13
authentication-tokens:1.4
backup:1.6.1
bitbucket-oauth:0.10
bitbucket:1.1.27
block-build-final-project:1.0
blueocean-autofavorite:1.2.4
blueocean-bitbucket-pipeline:1.24.6
blueocean-commons:1.24.6
blueocean-config:1.24.6
blueocean-core-js:1.24.6
blueocean-dashboard:1.24.6
blueocean-display-url:2.4.1
blueocean-events:1.24.6
blueocean-git-pipeline:1.24.6
blueocean-github-pipeline:1.24.6
blueocean-i18n:1.24.6
blueocean-jira:1.24.6
blueocean-jwt:1.24.6
blueocean-personalization:1.24.6
blueocean-pipeline-api-impl:1.24.6
blueocean-pipeline-editor:1.24.6
blueocean-pipeline-scm-api:1.24.6
blueocean-rest-impl:1.24.6
blueocean-rest:1.24.6
blueocean-web:1.24.6
blueocean:1.24.6
bootstrap4-api:4.6.0-3
bouncycastle-api:2.20
branch-api:2.6.3
build-blocker-plugin:1.7.7
build-timeout:1.20
categorized-view:1.10
checks-api:1.7.0
cloudbees-bitbucket-branch-source:2.9.8
cloudbees-folder:6.15
command-launcher:1.5
conditional-buildstep:1.4.1
copyartifact:1.46
credentials-binding:1.24
credentials:2.3.18
cucumber-reports:5.5.0
cucumber-testresult-plugin:0.10.1
cucumber-trends-report:1.3
discard-old-build:1.05
display-url-api:2.3.4
docker-commons:1.17
docker-workflow:1.26
durable-task:1.35
echarts-api:5.1.0-2
email-ext:2.82
external-monitor-job:1.7
favorite:2.3.3
font-awesome-api:5.15.2-2
git-client:3.7.1
git-server:1.9
git:4.7.1
gitbucket:0.8
github-api:1.123
github-branch-source:2.10.2
github-oauth:0.33
github:1.33.1
global-build-stats:1.5
gradle:1.36
groovy:2.3
handlebars:3.0.8
handy-uri-templates-2-api:2.1.8-1.0
hp-application-automation-tools-plugin:6.8
htmlpublisher:1.25
jackson2-api:2.12.3
javadoc:1.6
jdk-tool:1.5
jenkins-design-language:1.24.6
jira:3.2.1
jjwt-api:0.11.2-9.c8b45b8bb173
job-import-plugin:3.4
jobConfigHistory:2.27
join:1.21
jquery-detached:1.2.1
jquery:1.12.4-1
jquery3-api:3.6.0-1
jsch:0.1.55.2
junit:1.49
ldap:2.6
lockable-resources:2.10
mail-watcher-plugin:1.16
mailer:1.34
mapdb-api:1.0.9.0
matrix-auth:2.6.6
matrix-project:1.18
maven-plugin:3.10
mercurial:2.14
metrics:4.0.2.7
mock-security-realm:1.5
momentjs:1.1.1
monitoring:1.87.0
naginator:1.18.1
notification:1.14
oic-auth:1.8
okhttp-api:3.14.9
ownership:0.13.0
pam-auth:1.6
parameterized-trigger:2.40
pipeline-build-step:2.13
pipeline-github-lib:1.0
pipeline-graph-analysis:1.10
pipeline-input-step:2.12
pipeline-milestone-step:1.3.2
pipeline-model-api:1.8.4
pipeline-model-definition:1.8.4
pipeline-model-extensions:1.8.4
pipeline-rest-api:2.19
pipeline-stage-step:2.5
pipeline-stage-tags-metadata:1.8.4
pipeline-stage-view:2.19
plain-credentials:1.7
plugin-util-api:2.1.0
poll-mailbox-trigger-plugin:1.026
popper-api:1.16.1-2
postbuild-task:1.9
pubsub-light:1.13
purge-job-history:1.6
queue-cleanup:1.4
repository:1.3
resource-disposer:0.15
role-strategy:3.1.1
run-condition:1.5
scm-api:2.6.4
script-security:1.76
snakeyaml-api:1.27.0
sse-gateway:1.24
ssh-credentials:1.18.1
ssh-slaves:1.30.2
structs:1.22
subversion:2.14.0
support-core:2.73
testng-plugin:1.15
thinBackup:1.10
timestamper:1.12
token-macro:2.15
trilead-api:1.0.13
variant:1.4
view-job-filters:2.3
windows-slaves:1.7
workflow-aggregator:2.6
workflow-api:2.42
workflow-basic-steps:2.23
workflow-cps-global-lib:2.18
workflow-cps:2.90
workflow-durable-task-step:2.38
workflow-job:2.40
workflow-multibranch:2.23
workflow-scm-step:2.12
workflow-step-api:2.23
workflow-support:3.8
ws-cleanup:0.39
Result: [Plugin:ace-editor, Plugin:ant, Plugin:antisamy-markup-formatter, Plugin:apache-httpcomponents-client-4-api, Plugin:applitools-eyes, Plugin:authentication-tokens, Plugin:backup, Plugin:bitbucket-oauth, Plugin:bitbucket, Plugin:block-build-final-project, Plugin:blueocean-autofavorite, Plugin:blueocean-bitbucket-pipeline, Plugin:blueocean-commons, Plugin:blueocean-config, Plugin:blueocean-core-js, Plugin:blueocean-dashboard, Plugin:blueocean-display-url, Plugin:blueocean-events, Plugin:blueocean-git-pipeline, Plugin:blueocean-github-pipeline, Plugin:blueocean-i18n, Plugin:blueocean-jira, Plugin:blueocean-jwt, Plugin:blueocean-personalization, Plugin:blueocean-pipeline-api-impl, Plugin:blueocean-pipeline-editor, Plugin:blueocean-pipeline-scm-api, Plugin:blueocean-rest-impl, Plugin:blueocean-rest, Plugin:blueocean-web, Plugin:blueocean, Plugin:bootstrap4-api, Plugin:bouncycastle-api, Plugin:branch-api, Plugin:build-blocker-plugin, Plugin:build-timeout, Plugin:categorized-view, Plugin:checks-api, Plugin:cloudbees-bitbucket-branch-source, Plugin:cloudbees-folder, Plugin:command-launcher, Plugin:conditional-buildstep, Plugin:copyartifact, Plugin:credentials-binding, Plugin:credentials, Plugin:cucumber-reports, Plugin:cucumber-testresult-plugin, Plugin:cucumber-trends-report, Plugin:discard-old-build, Plugin:display-url-api, Plugin:docker-commons, Plugin:docker-workflow, Plugin:durable-task, Plugin:echarts-api, Plugin:email-ext, Plugin:external-monitor-job, Plugin:favorite, Plugin:font-awesome-api, Plugin:git-client, Plugin:git-server, Plugin:git, Plugin:gitbucket, Plugin:github-api, Plugin:github-branch-source, Plugin:github-oauth, Plugin:github, Plugin:global-build-stats, Plugin:gradle, Plugin:groovy, Plugin:handlebars, Plugin:handy-uri-templates-2-api, Plugin:hp-application-automation-tools-plugin, Plugin:htmlpublisher, Plugin:jackson2-api, Plugin:javadoc, Plugin:jdk-tool, Plugin:jenkins-design-language, Plugin:jira, Plugin:jjwt-api, Plugin:job-import-plugin, Plugin:jobConfigHistory, Plugin:join, Plugin:jquery-detached, Plugin:jquery, Plugin:jquery3-api, Plugin:jsch, Plugin:junit, Plugin:ldap, Plugin:lockable-resources, Plugin:mail-watcher-plugin, Plugin:mailer, Plugin:mapdb-api, Plugin:matrix-auth, Plugin:matrix-project, Plugin:maven-plugin, Plugin:mercurial, Plugin:metrics, Plugin:mock-security-realm, Plugin:momentjs, Plugin:monitoring, Plugin:naginator, Plugin:notification, Plugin:oic-auth, Plugin:okhttp-api, Plugin:ownership, Plugin:pam-auth, Plugin:parameterized-trigger, Plugin:pipeline-build-step, Plugin:pipeline-github-lib, Plugin:pipeline-graph-analysis, Plugin:pipeline-input-step, Plugin:pipeline-milestone-step, Plugin:pipeline-model-api, Plugin:pipeline-model-definition, Plugin:pipeline-model-extensions, Plugin:pipeline-rest-api, Plugin:pipeline-stage-step, Plugin:pipeline-stage-tags-metadata, Plugin:pipeline-stage-view, Plugin:plain-credentials, Plugin:plugin-util-api, Plugin:poll-mailbox-trigger-plugin, Plugin:popper-api, Plugin:postbuild-task, Plugin:pubsub-light, Plugin:purge-job-history, Plugin:queue-cleanup, Plugin:repository, Plugin:resource-disposer, Plugin:role-strategy, Plugin:run-condition, Plugin:scm-api, Plugin:script-security, Plugin:snakeyaml-api, Plugin:sse-gateway, Plugin:ssh-credentials, Plugin:ssh-slaves, Plugin:structs, Plugin:subversion, Plugin:support-core, Plugin:testng-plugin, Plugin:thinBackup, Plugin:timestamper, Plugin:token-macro, Plugin:trilead-api, Plugin:variant, Plugin:view-job-filters, Plugin:windows-slaves, Plugin:workflow-aggregator, Plugin:workflow-api, Plugin:workflow-basic-steps, Plugin:workflow-cps-global-lib, Plugin:workflow-cps, Plugin:workflow-durable-task-step, Plugin:workflow-job, Plugin:workflow-multibranch, Plugin:workflow-scm-step, Plugin:workflow-step-api, Plugin:workflow-support, Plugin:ws-cleanup]