Basically:

There are less Religion Tenets available (8 - 6 - 6 - 4) than the max amount of players (10). I have never encountered a problem where Tenets ran out before my Religion leveled up, but I've seen two people now report that's what is happening to them.

Easiest way to correct this problem is to have there be, at least, ten tenets to choose from at each level or allow players to pick tenets that have already been chosen by other players. As, right now, the Game expects there to only be 8 Religions, at maximum, that then decrease to 6, then 4. Which is a huge problem in cases where There are still eight religions active by tenet level 2, and a player can not force to end a turn because the game keeps asking them to choose a tenet that is not available.