Hi Joel,
according to this wiki entry: https://wiki.snapmaker.com/en/general/manual/technical_specifications_of_laser_module the maximum work area of the 40W is 320x350 mm without quick swap kit, i.e. the whole area. The QSK will reduce this to 320x335 mm.
That said, you can “squeeze” a bit more from the machine - you already get 340 in X it seems, and in Y you can also get a few mm - see here: Maximum Y Position 347mm?
And of course you gain another 15 mm in Y if you unscrew the QSK.
Indeed you will not get any warnings - the movements will just stop at the maximum point and continue as if all was fine… This will cause exactly your problem.
That said, I agree that Snapmaker does a poor job of giving correct dimensions and sizes… The Snapmaker 2.0 shop page even claims 350x350 mm work area in a very prominent way:
Misleading…
EDIT: Cross-posting with Wyphorn - Wyphorn’s link is the better one!
EDIT EDIT: Looking at this post: Maximum Y Position 347mm? - #10 by nweolu 350x350 is even legit 