This can happen sometimes when you “duplicate” images or tilemaps. (Like if you drag an image out of sorting else) This copying of data can sometimes lead to glitches like this in the editor. Things you can do:
1.Name all of your assets
2.Delete unused assets or duplicates of assets. Replace these duplicates with one central named version.
3.Don’t “duplicate” as frequently. Especially with tilemaps or longer animations. Instead you can go into an asset and use the box selector tool to select something you want to duplicate. Then use your copy shortcut to translate the image into text. You can then paste this where you want to copy it without fear of glitches/corruption.
This is one of makecodes most frustrating glitches. It can also lead to the seeming deletion of images. If it’s too horrible for you or you can’t fix it I recommend switching to JavaScript as I’ve never seen this happen there. Good Luck!