Let me know if that helps! I hope so since it was a pain for me that nobody suggested. I got frustrated with that one enough that I got a p1s but still decided to tear down the entire enter and put it together to see if it fixed the issue (it did) so I could give it to my buddy

If it’s a band one thing you can check is if the build plate is sufficiently torqued down. I spent ages chasing down a weird z issue, to the point where I converted my ender 3 z axis to being belt driven, and would still get really weird bands at certain heights. Turns out the bed was ever so slightly loose and at certain z heights would go into a tiny resonance frequency causing bands in the z axis. I’m not too familiar with the a1, but it’s a possibility that no matter what I researched I never saw mentioned