Hi I have posted this scenario before. I had z bands after I did a monthly maintenance. The reason I do this monthly is I use ABS only and it can cause problems.
So I eventually went back and re did the belt tensioning procedure. I made sure to loosen the four screws on the back but just loosen a little. Then I made patterns with the x gantry in corner to corner movements and then front to back at least 10 times. This helps to let the springs find the right tension for the belts.
After I did that I pushed the gantry all the way to the back and made sure both ends of the gantry was touching the back of the printer.
Then I just snugged up the screws a little.
Followed with a full calibration and a reboot after that.
Also after the reboot you will have to do another bed level and flow dynamic calibration.
This fixed my z banding. I do this every time now and it has never returned.
HTHs