Also note that with WIndows clients, having an AX chipset does not mean the client works with WiFi-6. That's driver and Windows version dependent.
And make sure the client doesn't pick the 2.4GHz band because it's stronger. Checking client capabilities as suggested may be a good start.
------------------------------
Herman Robers
------------------------
If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
------------------------------