Engines, Engine Plates, Locked Autostruts etc. When you merge two vessels in the editor this might happen after seperation during flight: https://imgur.com/a/6CzwGYi The solution/workourand is to always open first in the editor the upper/highest stage/part of your vessel then merge the later stages/other vessels under it.(The grandparent autostruts go up and not down). https://imgur.com/a/1Ne8p2E Please report this in bugtracker .I made an account but i have no idea how