Do you have packet captures? Logs? Other/more information? Do you see problems/degradation? What type of client? What type of AP?
The question outside it's context may be hard to answer except the generics that either an AP or client can only transmit if the channel is free. As the client and AP may be in a different location, and if there is interference close to the client, the client may not hear the AP or the channel is busy all the time and the client can't transmit.
------------------------------
Herman Robers
------------------------
If you have urgent issues, always contact your HPE Aruba Networking partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact HPE Aruba Networking TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or HPE Aruba Networking.
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.
------------------------------