In the past, builds used to process fine in Jenkins from Bitbucket Server using the atlassian-bitbucket-server-integration plugin and specifying "Optional SSH Credentials" (while leaving "Credentials (for build auth)" empty) in the Branch Sources > Bitbucket server settings.

After an upgrade to the specified versions, Jenkins will not properly access the repo until valid credentials have been specified in the "Credentials (for build auth)" field.

This broke several builds.  The "Credentials (for build auth)" must be a user account and their password (which regularly expires) or their personal access token.  Since this is tied to a user, they may leave the company and all builds will break (where the SSH access key is valid for the project and has a lifecycle that is not attached to any specific user).