It's not a big deal, but it seems like the number in the "Posts" column under Media -> Forum Attachments is not updating. It seems to only counter upwards. When I create 2 posts that use a certain attachment and delete one of those posts, the number is stuck at 2, even after emptying caches and updating everything through the wpForo dashboard.
This is a known issue and comes from MySQL version. As far as I know, the issue is fixed MySQL 8.0 version. It’s just statistic and doesn’t affect the way plugin work.
Also please note questions related to wpForo add-ons should be asked in gVectors.com forum here we support questions related to the wpForo plugin.