The UBO guys have recommended turning off other plugins (obviously, start by turning off everything, then turn stuff on slowly until you find what is conflicting).
Oh, and make sure you're on Firefox, not any chromium based browser (Edge, Chrome, Opera, Brave etc).
I've also seen suggestions that you should try removing any custom filters (can't remember if that's direct from the UBO guys or not)
That would just put an undue burden on the places that host the blocklists, for no good reason. Purge is something that only needs to be done manually in particular cases like this one.
It's being discussed as a solution to counter the changes Google is making on a daily basis, so that sounds like it's going to be needed moreso going forward.
Go to settings. Go to Filter Lists. Click purge all caches. Click update now.
That’s it, this message should disappear entirely.
I think there is going to be a time when ublock alone cannot simply program their way out of this, they will need help eventually from a completely different approach like anti ablock killers or some other app that hide the blocker itself from detection