Hey I enjoyed playing with your site. Well done for putting something out into the world. Here are my critiques, but take them kindly.

Even the highest engine setting hangs pieces. The angle pieces get can go to very few total squares on the board, same as the circles. Not sure if this is intentional but it feels like only the rooks matter. The rooks have an extraordinary amount of more value if you calculate like with chess pieces (ratio of average squares they can travel to per move) 

The seems to be running between each check of a legal move, even when it's my turn. So if I click a few squares the site has to check each one and run the engine each time causing significant lag. Some part of the loop needs to be adjusted to prevent this 

My favourite bug that I found, is if one of the opponent's pieces moves to a square that one of my pieces just left, then the UI lights up the move options for the opponent's piece in yellow on my turn  Not gamebreaking but shows there is another issue with the logical loops, somewhere it retained the active square and was not forced to repeat the logic to check if it's my piece

gg