Board Thread:Support Requests - Getting Technical/@comment-1828842-20201022174422/@comment-45117243-20201022181751

I see now. You have a custom JavaScript code in your common.js page which was used to manage those collapse classes. The code was written years ago by Kirkburn which is a memebr of Fandom staff, but was never updated to be comaptible with UCP.

Try changing all "collapsible" and "collapsed" in all the templates to the standard mediawiki collapsing classes - "mw-collapsible" and "mw-collapsed" - and let's see what happens.