I had the impression they already enforced it about a week ago, at that point the API no longer accepted older client versions.
The game rules are based on your client version. It’s you playing the game on your machine, your client doesn’t know anything about the client the opponent was using, it treats both parties the same.
The real problem here seems to be Lycantropy in combination with Deathmark. If you look at your screenshot, the game still thinks it’s the AI turn, the marker at the top is on the right side. As much as I understand it Lycantrophy and Deathmark both triggered and are just getting processed, except that one handler is no longer able to find the troop the other handler just removed, so the game gets stuck. We’ve had somewhat similar issues in the past, e.g. with Arachnean Weaver triggering the third trait while getting sacrificed on your turn.
Edit: Oops, meant the screenshot Whiskeyjack posted a bit further up.