Listview and search not working correctly and user list blank - Solved

Vtiger 7.5 (migrated from 7.4 and older). Php 8.1.2 and MySQL 8.0.32.

When I look at activities linked to a contact or organisation (listview) only the first page displays correctly. However if I try to go to subsequent pages or back to the first page, only the search line shows. No records are displayed.

The 'Assigned to' box in the search bar has a box with a cross in it. If I delete this cross, then the requested page is displayed correctly (but the box with the cross reappears). Also, the search does not return any results unless this box with the cross is deleted first.

When I delete the box with the cross then click in the 'Assigned to' box a dropdown list appears. Under 'Users' there are a number of blank lines (equal to the number of users) then all groups are displayed correctly.

I can't reproduce this behavoir on a clean install of V7.5. Does anybody have some suggestions as to how I can sort this on my migrated version?