Ah! Thanks so much for reporting this, we released an Arcade update last Friday and it looks like we broke some things in our blocks along the way. We’re aiming to have this fixed in the next day or so, in the meantime you can try the method described here:
or use the standalone set mySprite x to block:
to set the x and y. Sorry for the inconvenience, and hopefully it won’t be an issue for very long!