Symptoms
Non-admin users are not able to view/edit assignment groups and assignment rules as expected .
Release
ALL
Cause
One of the identified causes of the issue is the use of the plugin SolarWinds Alert Integration which adds some ACLs to the assignment group and assignment rules tables which can impact the behavior of some OOB features.
Resolution
If you are facing the symptoms mentioned above, double check if you have the plugin SolarWinds Alert Integration installed in the instance. If so, review all the ACLs added by this plugin in relation to the weird behavior that you are encountering.