Worth noting a workaround: just add a message to the assertion, e.g.

assert false : 'oh no!'

This looks happen in here:
https://github.com/jenkinsci/workflow-cps-plugin/blob/workflow-cps-2.17/src/main/java/org/jenkinsci/plugins/workflow/cps/CpsThreadGroup.java#L335

An exception occurs here, and codes to complete builds (such as calling fireCompletionHandlers) are skipped. This results builds not finish.

Fails to add ErrorAction as it fails to be serialize to disks (attached a full thread dump):

Caused by: java.lang.UnsupportedOperationException: Refusing to marshal org.codehaus.groovy.runtime.powerassert.PowerAssertionError for security reasons

threaddump_halt_by_assert.txt

Exception thrownd by assert false

error	PowerAssertionError  (id=128)	
	cause	PowerAssertionError  (id=128)	
	detailMessage	"assert false" (id=162)	
	stackTrace	StackTraceElement[0]  (id=166)	
	suppressedExceptions	Collections$UnmodifiableRandomAccessList<E>  (id=168)	

Exception thrownd by assert false: 'oh, no!'

error	AssertionError  (id=125)	
	cause	AssertionError  (id=125)	
	detailMessage	"oh, no!. Expression: assert false: 'oh, no!'" (id=163)	
	stackTrace	StackTraceElement[0]  (id=167)	
	suppressedExceptions	Collections$UnmodifiableRandomAccessList<E>  (id=169)	

Classes not to serialize are defined here:
https://github.com/jenkinsci/remoting/blob/remoting-2.62/src/main/java/hudson/remoting/ClassFilter.java#L56

Code changed in jenkins
User: ikedam
Path:
src/main/java/org/jenkinsci/plugins/workflow/actions/ErrorAction.java
src/test/java/org/jenkinsci/plugins/workflow/actions/ErrorActionTest.java
http://jenkins-ci.org/commit/workflow-api-plugin/9892fdffe0c3dfd34ba02b1edb0960f4c724b04d
Log:
[FIXED JENKINS-34488] Use ProxyException for exceptions that aren't serialized by XStream for security reasons

Code changed in jenkins
User: ikedam
Path:
src/main/java/org/jenkinsci/plugins/workflow/actions/ErrorAction.java
http://jenkins-ci.org/commit/workflow-api-plugin/7f2ed852fe0ffc119e8d5e8c7a408ddd35a81437
Log:
JENKINS-34488 Add null check to `isUnserializableException`

Code changed in jenkins
User: Jesse Glick
Path:
src/main/java/org/jenkinsci/plugins/workflow/actions/ErrorAction.java
src/test/java/org/jenkinsci/plugins/workflow/actions/ErrorActionTest.java
http://jenkins-ci.org/commit/workflow-api-plugin/18481659fcc4ee9f62fdbf07cd44aed373664832
Log:
Merge pull request #18 from ikedam/feature/JENKINS-34488_UnserializableException

JENKINS-34488 Use ProxyException for exceptions rejected by XStream

Code changed in jenkins
User: Jesse Glick
Path:
pipeline-model-definition/pom.xml
http://jenkins-ci.org/commit/pipeline-model-definition-plugin/4912a56312a45cf58dab1d0f5e4227ab9bb9fc00
Log:
Updating workflow-api dep to pick up JENKINS-34488 fix, making JENKINS-39134 easier to track.

Code changed in jenkins
User: Jesse Glick
Path:
pom.xml
src/main/java/org/jenkinsci/plugins/workflow/actions/ErrorAction.java
src/test/java/org/jenkinsci/plugins/workflow/actions/ErrorActionTest.java
http://jenkins-ci.org/commit/workflow-api-plugin/724456bd6c703b0d09dd9be5082e019af84cf4bc
Log:
[FIXED JENKINS-39346] Extend JENKINS-34488 fix to cover also nested exceptions.

Code changed in jenkins
User: Jesse Glick
Path:
src/main/java/org/jenkinsci/plugins/workflow/actions/ErrorAction.java
src/test/java/org/jenkinsci/plugins/workflow/actions/ErrorActionTest.java
http://jenkins-ci.org/commit/workflow-api-plugin/a48460ebdf7d03bedd82bb9e3e9de41481d58a4a
Log:
JENKINS-49025 Extending JENKINS-34488 fix yet again; JENKINS-39346 only considered causes, but other Throwable fields could also be unserializable.

Code changed in jenkins
User: Andrew Bayer
Path:
src/main/java/org/jenkinsci/plugins/workflow/actions/ErrorAction.java
src/test/java/org/jenkinsci/plugins/workflow/actions/ErrorActionTest.java
http://jenkins-ci.org/commit/workflow-api-plugin/43fc2f234bdddbdbdbf72c1844cc5750c88618c0
Log:
Merge pull request #64 from jglick/nested-error-fields-JENKINS-49025

JENKINS-49025 Extending JENKINS-34488 fix yet again

Compare: https://github.com/jenkinsci/workflow-api-plugin/compare/1f5461aa99df...43fc2f234bdd