Okay, autosave isn't the most trustworthy way to save.
I recommend you to save your drawing to your computer instead of to the tool itself. If you save it to the computer there is a 95% it will perfectly upload to the site again.
And yes, that percentage was made up. But the chances are high!
I'm new here. Yesterday i get so much effort in a drawing, but i havent finished. So i saved it in a folder, and was thinking that i cant finnish today. But if i try to reload, only the message appears, that there's no drawing! I read, that there is autosave from time to timme, and i have saved it additionally!