Hi Florian, thank you for the detailed description. Since it seems you've narrowed down the issue to the new firmware version, I'd like to do the following:
1.
Pull tech data from an AP having these issues that is currently using firmware version 10.4r3.
1.a. If you can note the MAC address of a device having issues while the AP is on the newer firmware version, that will help narrow down which logs we need to look at here.
2. Revert the same AP back to the previously working firmware version
3. Wait a few minutes for the AP to pass traffic with the new firmware version, then pull a second tech data file so we can compare how things are working between the two APs.
4. If possible, open a support case on our
Extreme Portal, and attach these two tech data files to the case. If you aren't able to open a support case right now, please feel free to send the tech data files to me at community@extremenetworks.com, and I'll let you know what I'm able to find. Just so you are aware, you'll get better and faster help from a support case. It's been a few years since I worked support cases; I'll do my best to help you but you'd be better off with a current technician via a case.