rip protogen (corrupted XML)

You might try creating a new sandbox and see if that improves performance.

edit 3: the game goes slower after the problem

@AndrewGarrison no , im not using mods, I even uninstalled those that I did

I see. Unfortunately, if the file is empty and without any backups there is nothing we can do to help fix the issue at this point. Whatever happened initially that caused the file to fail to be written has already happened. I'm sorry for the bad news. Are you using any mods?

@AndrewGarrison yep

So there is a file for your protogen craft but it is empty?

@AndrewGarrison I see XML files but those of my plane are empty

@AndrewGarrison no, only in one

Also, are you playing SR2 on multiple computers?

I'm really sorry to hear that. What files/folders do you see here:

C:/Users/%USERNAME%/AppData/LocalLow/Jundroo/SimpleRockets 2/UserData/CraftDesigns/

edit 2 :my sandbox also got deleted

@AndrewGarrison

edit: steam also eliminated the game but not the files