Hello, mobile user here.
After messing with the editor, I actually have no idea how this happens, but it has happenes multiple times. The designer just breaks down for almost no reason, requiring closing and opening of the game to fix. You can't move a part: it just stays in the same spot. Sliders break, they seem to visually change but the actual shown stat doesn't change. Saving and loading crafts doesn't work. It's just a strange mess. This can be a large issue; resetting the whole progress of a well built rocket.
I apologize for this maybe being in the wrong tags (Just made this account a few minutes ago, still getting used to everything here on the forums.)
I'll be sure to try if it happens. It happens very rarely when doing strange things like trying to place something somewhere weird. (I think the game gets very confused of where to place a part)