Question Centering a star

My mount is an Avalon StargGo type: Linear HQStarGo 7.0.8 Firmware 6.4.0 Ascom Driver 7.1.2.0The mount works very well. The guiding is perfect: PHD2 is not even needed.This has been happening for a few weeks:• I start with a classic Home Position, go to a star, center the star and do a sinc (Starry Night Pro) but on the screen the position of the telescope and the star are not the same. I do this with a few other stars but the deviation remains. The deviation is not large but enough to not get a next star in the image. This is very annoying when centering a nebula.• The same happens in Stellarium.• My location is OK. Polar Alignment with ScarpCap Polar Align.• I have removed StarGo and done a new installation but the problem remains.What can I do?