Force stop and clear cache if you're not seeing the new update
Pretty much the title. If sync isn't prompting you to update at launch when there's a new update available just force stop and clear your cache. Next launch you should be prompted to update.
Posted from sync!
It should only prompt you if the play store realizes there's an update available.
And the play store didn't realize an update was available until I cleared the cache.
That's impossible. The Play Store app doesn't care about Sync's cache. That was simply coincidence.
Cleaning the Play Store app's cache on the other hand might help.