I was one of the users who initially reported this problem on the newsgroup. I have been using the mozilla clients for probably 20 years, or as long as I can remember anyway. I have always selected view/ sort by/subject,ascending, and threaded. Then view/threads/unread. Has always worked for me until ver 92. Happens on both win 10 and win 7 machine. Half of the groups I subscribe to have the issue of these settings not sticking, the other half work just fine.
Today I tried subscribing to some new groups to see if I could figure out what sequence was causing this problem. No matter what I tried as far as sorting, when I marked things as read, numbers of groups I subscribed to at a time, any variable I could think of, nothing produced the error and all new groups immediately worked as they should and always have.
I tried unsubscribing from one of the groups this error was manifesting itself, closing down, and then resubscribing. It again loaded all the messages as new, and then worked through what I suppose was my rules and filtering file that was left behind. upon setting the rules as I wanted, it went back to working as it did before and would not save the settings. I'm wondering if somehow the the retained filter rules file is causing this.
I know you need to find what the problem is, but I think to make the client usable for now I have to continue seeing if this might be of value to me. I guess what users like me would need to know is what specific files could we isolate to see if removing them eliminates any chance it is being caused by these retained past files and then reinserting them to see if it reappears. That might at least narrow down the location of where the problem is coming from??? If it is these files, we could always build new filters.