FWIW, my Outlook suddenly began failing last night (it was never a problem on my first two hard resets, the one in question being the third). Failing in the sense that I was not able to reply to emails, as soon as I'd touch in the To/Subject/Body, it would send me back to the Start Screen. I tried removing and reinstalling but also could not find the app .... moments later, it was reinstalled but didn't work any better.
I did another hard reset last night (because I am not able to roll back to Win 8.1 with the rollback tool and was hoping the problem inlay there) and while it's the most stable the rest of the apps on the phone are, MS Outlook now kicks me out as soon as it syncs (ellipses stop moving and it kicks me to the Start).
This is on a Lumia 928