You are not compensating for the line height you are allowing for physics and math.
If you placed the plug and socket at an imagined height of 100.1mm, and you are printing at 0.2mm layer heights that 100.1mm position isn’t 100.0mm or 100.2mm, so the slicer has to guess. It could go above to 100.2mm or below at 100.0mm.
It is like you trying to cross a river by jumping on rocks spaced equally apart, if you jump in between two rocks, you are not going to have a great experience.
Anything is possible, but, ignoring the obvious and hoping it is something else isn’t an ideal way to determine a cause.
If this is the reason, nothing else you do will fix it.
Assuming you designed the model, checking the z-position shouldn’t be difficult and fixing the problem can’t be as difficult as creating the original model.