Have you tried the 10.5.1.1 beta reinstalling over the top (don't uninstall first; that would wipe the config and shouldn't be needed) and then rebooting? It's possible the update did not fully install or something happened to go wrong during the post-update reboot which may be fixed by rebooting again (happens more often than you'd think; it's also possible another change was pending the reboot and it's that which is causing the problem rather than the Opus update itself).
If reinstalling 10.5.1.1 beta over the top of itself & rebooting does not solve it, do you still see the problem if you go back to the 10.5.1.0 stable release? If the problem remains in the stable release then it's just coincidence that it started after installing the new beta, and the Crash, exit or high CPU usage when viewing certain directories guide is your best bet for tracking it down. (It's most likely a shell extension going wrong.)
The only change in the 10.5.1.1 beta I can think of which might be related is the new ability for labels to change file icons. Do you have any labels defined under Preferences / Favorites and Recent / File and Folder Labels? If so, try disabling them all to see if it makes a difference (and if it does, let us know their details so we can investigate).
(Maybe the beta release notes have some clues that might match the directories you are looking at. e.g. There were changes to JPEG metadata handling and to what happens if you hide file extensions or show them as a separate column, so the crashes seem to happen when dealing with that sort of thing then those changes may be related, but it seems unlikely unless there is that kind of correlation.)
If you only see the crash sometime after dragging files to Opus from another program, try setting Preferences / Miscellaneous / Advanced: dragdrop_async = False to see if it helps, as there were some changes there as well. They'd only matter during or shortly after drops from other programs, though.