As stated above from other post, casting spell will fix it. It’s the whole board that freeze, everything is working fine. Don’t cast Krystenax (I assume any spells that required to choose gems on the board as well) though, or the whole game will freeze, with hard restart as the only way out.
And if you don’t have any spells available when this happened, you’re screwed. Still it can be avoided by not cast Krystenax as a finishing move.