Here is my set up - since I don't know for sure which settings are causing the lockup, I'll probably mention irrelevant things: consistently, there are some times that it just happens by itself after some period of time (sometimes a few moments, sometimes a few hours; sometimes while using it, sometimes after I've been away from it for a few hours).
I have searched all over, and there seem to be many with similar (apparently) problem, and found numerous "solutions" (some even more cargocultish than mine), but so far none of them worked.
(I'm thinking downloading a large chunk via http and getting a small packet loss might drive Outlook crazy) Check the size of the folders on disk versus the compress, indexing and auto-clean-up properties. I had also irregular freezes, created new accounts from scratch, started outlook in safe mode , diasbled ALL add-ins, disabled hardware acceleration , ran scanpst countless times on all pst's.
As near as I can tell, it happens to people who have Office 2016, licensed through a business Office 365 subscription. The Office updates are unpredictable, completely untethered from any day of the week, and we are given no warning when they are going to be installed. Nothing will make Outlook get past the “processing” screen. I uninstalled Office 64bit and installed Office 2016 32bit. Suprised that it was so difficult to make work on Outlook.It has come to our attention that many Outlook 2013 and Office 365 users are having issues within synchronizing IMAP folders recently.I would like to have all 3 accounts enabled, ideally in several groups (e.g.pull down only important folders in a group with short interval, and all other folders in a longer interval) - obviously without freezing up at all. Also, it seems you might have connectivity problems.