No limit. Probably not your machine fault either. Someone did encounter lag and crashes but that doesn't seem like the same. I guess something did go wrong there. It is still highlighting that one tile so looks like it somehow got stuck in that mode. Looks suspiciously like the bug (that I already fixed) where you hold a card while the character is still moving and stepping on purple recycles that card from your hand locking the game in a weird state. Might be something similar...
And that is actually 59 million 😅