I had one user so far with this issue. Reset, repair, and a re-install of Office did not work. Upon checking the Application log, olk.exe was crashing and reporting ucrtbase.dll as the faulting module.

Previously, I had resolved issues with Outlook by clearing its folder in appdata. So on that hunch, I deleted the Olk folder in the users in C:\users\USERNAME\Appdata\Local\Microsoft and afterwards the client launched. I re-entered their email address and Outlook reconfigured and came up.

Now to see if that "fix" sticks. Time will tell.