https://bugs.winehq.org/show_bug.cgi?id=45814
--- Comment #3 from Storm Engineer hewanci@gmail.com --- (In reply to Maciej Stanczew from comment #1)
It's enough to delete a single file, 'drive_c/ProgramData/Battle.net/Agent/product.db'
Indeed, that is the offender.
So it seems that what triggers the problem is if there is an update for anything - but that the Battle net app itself or any of the games, before the App starts.
My theory is that the reason I had it happen after updating battle net was that the update for it arrived while it was already running, it updated fine, but game updates might have only been triggered once the App was updated, which is why after restarting the condition for an update being available before the App starts was met.
I keep an eye on it. The last two times it happened I had an App update and a game update ready respectively, before the App launched.