Forum Application 2.2.1 Extension not loading on XWiki 10.4

I installed the Forum Application 2.2.1 on my XWiki 10.4. Most of it seems to be working well, but the front landing page of the Forum (All Forums" listing) doesn’t seem to be loading the list of active available forums. Take note in the screenshot. I understand 2.2.1 has been tested only with the stable XWIKI release, and 10.4 is not officially tested - but is there a way I can modify something in the velocity of the templates to get this to work? We have already invested a lot in getting 10.4 running, and don’t want to roll back to 9.x.2018-10-26_1417

This was happening due to stale forum entries from a previous installation. After deleting those entries through the wiki level Page Index, it started working.