Alexvs - you need to assert which ring is moving first. The adjustment collar or the calibration ring.
Calibration does not influence, in any way, in he gap between the top burr and the lower burr. Example, if you grind some coffee at you current setting, and then move the calibration ring to the opposite extreme, your coffee will still be ground in the exact same way as before. The calibration mark is a mere reference point. Nothing more.
To check which one is moving, you could add a little sticker to the metal collar (adjustment collar) and see if that moves up or down against the numbers on the dial.
If you can confirm it’s your black ring that keeps moving, I would contact Niche and ask for a solution to your problem - this is a minor issue, but annoying. If it’s the collar, I’d contact Niche for a replacement, as this might be some more involved. Although, re-reading your posts, you only seem to have issues after recalibrating, implying that the grinder is not loosing its grinding setting at all - only that the black calibration ring is moving when it shouldn’t.