It's not a perfect science like
D3LTA said, some machines even from the same company have different quirks. Z-banding could be mechanical in the frame wobbling back and forth, rocking of the print head due to rollers or rails not being tight, belts being loose, stepper issues, printing too fast, a wobbly buildplate, temperature changes in the hotend, temperature changes in the room, the list goes on.
If you do change something when troubleshooting, only do one major change at a time so you can assess if it helped or not. I've added a few modifications to these and I'll slowly keep upgrading them until they finally give up and call it quits.
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