At some point during development I accidentally duplicated my tilemap. While this did not change the look of my game at first glance, it introduced a bunch of weird bugs as everything in the game existed twice now. You could walk over a key, pick it up and walk away and there would be still one key lying on the ground. You could unlock a path with that key, but the barrier would remain visible. And after that, one of the two player characters (who originally where in the exact same spot) could walk over the barrier, but the other could not. Scratched my head about this for like 5 minutes, before figuring it out.
My game: https://njamster.itch.io/wonkey (playable in browser, not mobile friendly)