If you can join me on my Discord, it'll be easier to chat and share screenshots to sort this out. You can join here:
If not, we'll continue here. Here's my initial thoughts:
Do you press Save All to save?
If so, then does your level save to disk at all? It should appear in the Drawings or Extras folder of your project.
Does the number of frames matter? If you draw 20 frames, save, close, reopen, does it work?