Ok so castle's multiplayer system is a bit wonky so there's a few bugs here and there, if you find any of these please do what's said below
1. Sometime when trying to capture a checker instead of the tile in which the checker is in being highlighted in yellow it insteads remains blue, if this happens try to move to another checker free tile, this should fix it
2. When a checker gets crowned for some reason it gains the ability to move indefinitely, when this happens try to move another checker instead.