Ok this became an issue and users started having problems one after the other.Don't think i can make a good how-to out of this,maybe someone else can . So i put it here and maybe if the mods find this useful can move it elsewhere or delete it.
I believe this workaround is for cases like mine where outlook has been manually configured with MS servers for 365.
So after the upgrade, having connectivity problems, what worked for me was this :
Delete profile
open outlook
give a random name
get to the auto-discover screen (most important part)
give name,email and password
if all is green after that.Its good to go.
Hope it helps someone.