Kerbal Space Program

I try to find simple words:

1. I launch a sat-deployer vessel, so a rocket that carries multiple relay satellites
2. I go into resonant orbit and deploy them all
3. One after the other I bring them to final orbit
4. Afterwards they're nicely distributed around the celestial body, like 4 relay satellites are seperated by 90°
5. Later, after doing other stuff, launching other vessels etc. pp. - at least one of them moved around and is next to another one of the same "group"

1. they all had the same parameters, like apogee, perigee, inclination, surface speed ... so they should stay stable for a very long time
2. but just after a few ingame weeks or even days this issue occurs
3. it's not that the "special" vessel continues moving in a different orbit - it just stays where it is after the "jump", relatively spoken
4. so it "jumped" around the plane and settled down next to a brother for no reason

Imho this has to do with the fact that "once" all the deployed vessels were in the same physics range.

A screenshot:
https://cdn.discordapp.com/attachments/457294487677435904/514120405447868445/screenshot_2018-11-19--17-50-09.png
In this case even 2 of the 4 relay sats are displaced.

Reproduce?

Set a constellation, do other stuff, do several scene changes and check then and when.