I actually had this same issue that sometimes i noticed that my simucube 1 was losing centering. Both in SImucube configuration software so i needed to set first new center for wheel in Simucube configuration and then recalibrate in Iracing. I have small mige with Biss C encoder.
But i think i noticed what was causing it today.
I am turning power off for nightime (i have remote controlled power plugs) from both VR basestations and also from extra PC case where i have Simucube PSU and boards and also fans.
So when i start my gaming PC and also power up Simcube board it starts to rotate wheel.
Some kind of starting sequnce what wheels seems to be doing perhaps to place it to center where it was left. If i same time when sequence is running start Simucube configuration software centering of wheel goes off.
When i wait some tens of seconds after powering Simcube and Mige and let it run rotate wheel and then start Simucube configuration Tool no centering is lost.