Hello,
Since the Shatteted PD updates of the crystal caves (including beta versions), it seems like the game "lags" as in, seems to skip frames without actually freezing. This happens starting from the 6th level, not before, and stays the rest of the game. The main menu also seems to have the background animations sort of skip the same way but in a less obvious way.
This makes the game a bit annoying to play as sometimes you try to, let's say, attack, nothing happens so you press again, and suddenly you move where the enemy (who died during the frame skip) previously was, causing a lot of various unintended consequences. The problem shouldn't be with my phone considering that my system did not change and the game worked perfectly before updating.
Something similar happened to me in the latest build while I was chasing the Gnoll Geomancer (who is much easier than the crystal boss imo). My character moved halfway along the path I was going and stopped moving (the walk animation was still playing tho).
In my case everything visually freezes but the game keeps on processing things, so tapping during the freeze will trigger (often unintended) actions.
It also is sort of constant, with small freezes like that every few seconds, and seems to get worse the deeper I go.