I apologize in advance if this is known, but all the topics I can find for 1.5+ refer to lock-ups after No More Moves; however, I have found a different lock-up that seems to happen to me consistently that is not related to this situation.
At least three times since 1.5.1 has released I have encountered a lock-up in the following circumstances:
Opponent starts turn with enough loyalty to perform their ability, which they do.
They then get enough new loyalty or have enough left that they can perform an ability again.
They make a 5 gem match, giving them 1 Extra Swipe.
Instead of performing this swipe, the game hangs and the only thing that can be done is to quit.
My assumption, based on these circumstances, is that the game is trying to perform the ability again in the round, but cannot and therefore enters an infinite loop or fault state that it cannot recover from.