The user ID is a piece of email. It is PII. To define how it's broken is to describe a list of specific actions the user did to the private information in their account causing the UI to be broken.
If training is such a problem, I don't understand why we solve the problem by obviating such training and make the issue tracking system an acceptable storage medium for PII?
Because you were the one that said you needed granular RBAC to limit who has visibility of what issues!