We upgraded from Jenkins 1.170 to Jenkins 1.90 yesterday afternoon and initially saw no issues, but this morning found that all admin users were seeing a partial stack track on any Jenkins page they tried to load. This was traced back to the administrative monitors and from there we discovered that disabling the Cron Triggers Monitor (under Configuration -> Administrative monitors configuration) resolves the issue and enabling causes the issue to return. We assume this could be related to the recent issue 54854, resolved in Jenkins 2.189. Attached are both a screenshot of what we saw when this error and a text file containing the full stack trace.