The fact that it is occurring several layers up from the base could also mean that your ACME nuts aren’t free to move in their slot in the X end clamps as freely as they need to be able to. Also check the Z axis couplers on both sides for damage. if those rods are being forced to one side or the other every layer raise, you can get an effect similar to that if the ACME screws aren’t able to deflect to absorb the unwanted motion.
Aside from that, which of the upgrades have you made, if any? The Ao-101 should already have the Y axis belt tensioner, 16 tooth pulley and the lower x clamps in place. The carriage upgrade should also improve stability, that one was released after the last of the AO-101’s were sold so you probably don’t have that one yet. the AO-TAZ mod helps with accuracy quite a bit, but it is complicated to print and install.