Adjusting forum/activity page?
Using Jamroom
The list is to show all posts made by that user.
The template for that list is the jrForum/templates/activity.tpl and the page break is controlled by the page break set in your ACP > Profiles > Forum > Global Config > Page Settings > Topics Per Index Page ( /admin/global/section=page+settings )
The pagination that was messed up on your site was due to an outdated jrCore_list_pager.tpl in your skin directory, I've updated it in your ACP > Skins > Template section. ( /core/skin_admin/templates/skin=mdFOTMD_June15_2020 )
Hope this helps!