We already know that Nintendo uploaded Super Mario Maker 2 courses are very fond of removing, usually to break the rules regarding disruptions, abusive content or sometimes for no clear reason However, it turns out that your layers may also be deleted if they have not even been uploaded.
Kotaku reports that after creating a layer that contains the "black hole" error, users can overlay elements and clone endlessly – it was soon deleted. The removal was done after saving the level (without uploading) and returning to the Coursebot menu. The following screenshot was presented.
In essence, it seems that the game can detect glitches in your course and clears them immediately. No matter how long you have been at the level, it seems that it could be lost forever. Of course, if you purposely try to create glitches in the game, this is pretty understandable, but the users reported the problem without knowingly doing anything wrong.
In some cases, the game has allowed the user to re-enter the level and remove any intrusive parts. However, this seems to be the case only if the error occurs during the save process and not after the course has been completely saved.
If you want to play with glitches, you should be careful with glitches creations that you are proud of; Hopefully, not too many innocent players will be affected.