Wired test :
Have you tried using the same VLAN you are using on the VAP while connect directly into controller and doing the same test ?
Also run the following command to make there's no layer 1 issue show port stats and see if there's any errors and perform the same on your uplink .
This way you can eliminate that there's no issues all the back to your core connection .
And also will allow to create a baseline from a wired perspective back to your server or out to the Internet
RF health :
Do the following
show ap arm rf-summary ap-name <apname>
Show ap arm history ap-name <apname>
These two command will give you an idea if you have any RF issues
What AOS do you have installed ?
How do you have your connection setup back to the uplink ?