Thats actually very weird... I'd like to try and help you out but I don't really know how to fix that issue... All I can probably say and recommend is try to download and use a save that has 100 courses as the max (with possibility all or most of the amiibo costumes) and then use SaveMii to add it on your game, but it will most likely erase all of your levels if you do that
Super Mario Maker Community
