testcommonswiki and labswiki DB db1131 have the removed cuc_user and cuc_user_text columns as well as the associated index cuc_user_ip_time in the table cu_changes. These columns and index were removed from production wikis in T328817: Drop cuc_user and cuc_user_text from cu_changes in wmf wikis, but this wiki was missed.

This can be seen in the drift tracker report at https://drift-tracker.toolforge.org/report/checkuser/, including the relevant DB hosts.

1. ALTERs to run: https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/CheckUser/+/c50a5cbc/schema/mysql/patch-cu_changes-drop-cuc_user.sql
2. Where to run those changes: testcommonswiki and labswiki DB db1131
3. When to run those changes: At any time
4. If the schema change is backwards compatible: Yes.
5. If the schema change has been tested already on some of the test/beta wikis: Schema change is applied to all production wikis, except from testcommonswiki and labswiki DB db1131.