Well done implementation of chess figure movement rules - for my taste they all have a bit too much hitpoints… i mean, i could only kill pawns and one single bishop all others were just alive for too long.
Yes the bug happened mid-game at some point when I got hit by an opponent the first time - from that moment on my shots passed through everything. Maybe this is a hint to the origin of the bug.
Overall, nicely done, congratulations! oh, and the background endless chessboard texture is well done! fits perfect.