I've played Civ 5, with and without DLCs for over 15,000 hours, and have never had a problem founding a religion. Am trying three DLC options, for the first time: Zootopia civilization (my civ); Dalek civilization (computer); Cybermen civilization (computer).
On turn 20, found enough faith in a ruin to get a pantheon. I also built Stonehenge. So I know the computer sides haven't founded all the available religions.
I just got a great prophet, and the DLC has the same odd quirk for all units, saying it's earned a promotion. No button available for using the prophet to found a religion.
I'm hoping someone has found a hotkey or keyboard combo that commits the prophet to founding a religion.
Oh, and yes, the prophet is in my one city.