On a number of occasions over the last couple of years I have finished work on one computer but later (eg following day) found that those changes hadn't synced down to my other machine.
The reason appeared to be that a CC Desktop App had been released. Once I had updated, the file sync completed normally.
This might be vaguely-reasonable if the app had not been updated recently and was now obsolete. But not for single version updates. And in any case, sync really shouldn't be frozen by an update notification. One expects files to just sync quietly, but this exposes the user to editing old versions of synced files.
So please, notify the user that an update is required, but allow file syncing to proceed as normal.