Hey there @Krillblr! It’s possible the asset reference was broken. First I’d back your project up, and give some of the solutions in the thread Ram referenced, especially the final one where you delete the asset in your file structure, then create a new one, then overwrite that in your file system with your actual map. You may also have an autosave of the map that is recognized inside your Saved/Autosaves folder in your project.