Thunderbird operations suddenly at a crawl.
Windows 10 64 bit, oodles of resources (32 G ram).
Was always pretty snappy. Suddenly moving or deleting messages takes 5 to 10 seconds, rather than almost immediate.
Nothing else on my system shows similar behavior, only TB.
Interestingly, deleting messages in local folders is still instantaneous. It is only from "inbox" that I seem to be having a problem.