On my Win 10 Pro system, I did my usual full profile backup - was running the 02/02/2020 64-bit build from Bill - and uninstall, then installed today's 02/04/2020 Windows 64-bit build from Bill... as frg notes, these seem to have been done way earlier than Bill's usual schedule.
After I am asked for my master password, I supply it, and the email client comes up first - but with some issues: the left pane has the full normal tree structure with my various servers/accounts, but NO message counts - and the right [message] pane is EMPTY.
While I can still use the browser - including all of my tabs, apparently properly restored - after about 2 minutes, I will see a crash. It seems to be trying - for some reason - to be rebuilding the MSF (index) files when it dies.
I have repeated this - each time, restoring my backed-up profile before starting SeaMonkey - a number of times, and it is "solid".
I allowed a few of the crashes to be reported, but as I don't know where to get the links, I have no pointers to specific crashes.
I am happy to do any requested tests... I do hope my backup made with the 02/02/2020 build is not itself bogus - but in any case, I can restore any emails from the Inbox file the "hard way".
Finally, yes, I know I was supposed to be saving builds, but as they are downloaded directly to my RAM-drive based tmp, they sometimes are lost when I forget and do a reboot - if this is going to be a longer outage, I would be grateful if someone could post the 02/02/2020 Windows 64-bit build somewhere accessible... it at least worked AFAICT for my purposes.
Thanks!
On vacation and up late and down late too. Suits me better.