Soybean
Uh, do you try to swap two chess?
The other chess will be kicked off the board when one chess occupied it's space (the same x,y,z), the kicked chess is no longer at board and it could not "move" on the board.
Board plugin has "action: swap" to swap two chess in one action.
Or you could assign logic Z of chess to it's UID, so that all chess will never occupy to each other, then they will never be kicked off, and could move to any (x,y) at board.