I lost my Wallpaper

i am working with my Wallpaper, if i save and exit, after few minutes, it was change my project like this automatically why? is it bug or what?

I don't know why happen this, you can tap in the rounded arrow icon and here you have the last 10 saves of your work, tap on one of the saves and this are going to load this save in your editor.

yeah, i am able to retry, and get back my Wallpaper...but why it happen. bug?

I don't see this problem before, I don't think that is a bug.