PSA: I should have checked my nuts.

Sorry, couldn't resist the clickbait title, but yes, THOSE should be checked from time to time, too.

But the PSA I want to say is: Check your printer for mechanical problems if you have trouble. It might not be obvious in the first place.

In this case my Ender 3 Pro with sprite was printing a horrible first layer and the z offset was never right - when it looked ok on the left side of the x axis it was off on the right side and vice versa. (Regardless of endless tries of bed tramming and using a bed mesh)

It turned out I had the eccentric nut on the right side of the gantry tightend too much when mounting the sprite, so the right side of the gantry was not moving freely enough.

Now I adjusted the eccentric nut, so I can juuuuust turn the wheel with my finger a bit, maybe a bit looser that what was explained in this video: https://www.youtube.com/watch?v=GsEdU8ZtI6U

(And people, don't purchase a single Z axis printer if you can avoid it. When I bought my Ender there was a HUGE price difference to dual Z, but nowadays thigs look much better)