September - last edited September
Same problem here.
For whatever reason the formations on Switch are sometimes different than other platforms. I assume the check for validity on EA's end after submit is looking for a squad that matches the other platforms. Not to stick up for EA or anything but I would assume this is actually a bug on Nintendo's side porting the game... Not exactly a "fix" but if you can figure out what players satisfy the requirements for both formations it will accept your squad.