From what I understand, UserTags is a fairly complex dev script given all the customization options. In the past, I have been able to troubleshoot errors and fix them just fine. However, this is a strange case which seems to have appeared late last year, perhaps when core JavaScript was moved to a different name. Though, I have tried the newly named core config with the import and it still does not function—unless it is in personal JS. I cannot find a solution thus far.
The Common.js for the wiki with the problem can be found here.