IMO it was pretty slight push. Much heavier pushing is allowed IMO. That's typical ball challenge, players push each other, that was nothing out of ordinary. The Bastoni-Ranieri case was they both held each other, it wasn't one-sided.
Sommer case, I don't know the exact rules about that but Sommer got the ball clearly before the first hit Nzola's head. It's a dangerous play but then on the other hand, how goalie should go for such ball? I don't think that's a foul, just an unlucky situation where the attacker goes for the ball aswell and gets the followthrough of goalie's save. But as said, I don't know the exact rules and how those situations should be interpreted. Wouldn't be surprised there was an effect of already ruling out two cases against Fiorentina earlier in the match.
edit. But yeah I can accept a penalty to be called from that. It was a heavy punch to the head in the end.