Merge users not possible from UI or CLI

[per1234]

I encountered a problem like this and was able to find the cause and solution. I thought I should add a note here in case my findings might help anyone else who suffers the same and finds this topic through their research.

I have shared it here:

I'm attempting to merge user accounts

I encountered a problem like this and thought I should share my findings here in case it might help anyone else who experiences it. In my case, the account merge operation hung forever with the “Merge progress” dialog cycling back and forth between the “Changing post ownership…” and “Updating username…” messages. From looking at the staff action logs (/admin/logs/staff_action_logs), I could see that, although the ownership of many posts was transferred immediately after I triggered the merge…