Whenever I interlock something, and I dome back to it later, its somewhat un aligned, when it was perfect before. The way I do it is I set the object and set a couple of markers to know exactly where to put it, and i set the first object to not place at start, then i do a new round and place the new object. Is there another way to do it that is better in some way? This is on sandbox by the way.
Sandbox has been known to have this problem. There is no other effective way to interlock. What I recommend is just to let it be and if it gets to out of hand then do the interlock over when you are almost done with the map.
An object will snap to the last position you had it in when you last rotated it with the trigger if you save changes while your holding it.