Noncompliant query leads to (semi-)random sorting and failing unit test CRM_Case_BAO_CaseTest::testSortByCaseContact
This doesn't seem to come up on any commonly used screens but something has changed recently, either in mysql on the test sites or somewhere else, that is exposing a problem that has always been there in the query described at https://github.com/civicrm/civicrm-core/pull/17702#issuecomment-650777728 with regards to full-groupby. See also https://github.com/civicrm/civicrm-core/pull/17705.
At the moment it just seems to be causing CRM_Case_BAO_CaseTest::testSortByCaseContact to fail on every PR. I did some r-runs on one of the recent test sites for case dashboard/dashlet/find cases etc, and didn't see any (new) problems.