Improve unknown mark association changes page
At the moment that page doesn't bring much useful information except that some new/old associations were created/removed. Like with unsafe mark association changes (#8241) I suppose that the most valuable information at the unknown mark association changes page will be changes in all problems for affected unknown reports. Likely this will require one more cache that will hold information on all problems for all unknown reports.
BTW, information on all problems is welcome at the unknown reports list page. This is also very similar to unsafe reports.