Hey Fraser,
the XR1000 with firmware 1.0.0.52_1.0.38 does not have an option for enabling/disabling WMM in Wireless setup or Advanced Wireless settings. I would hope and assume it is enabled in the code, but doesn't allow you to change it on the interface.
The Netgear Nighthawk RAX43 however does allow you to enable/disable WMM in the QoS settings on firmware 1.0.2.72.
An interesting note, I have noticed that configuring both the Netgear RAX43 and XR1000 QoS congestion controls have the same issue. The wireless devices throughout the office do not obey the congestion rules, but the wired devices do.
I followed your other suggestions as well such as toggling CC never/always, resting distributions, verifying Share Excess enabled, and disabled all Traffic Prioritization rules, which currently is only the DUMA classified games rule. I also played around with just about every setting I could see, such as disabling AX, toggling settings such as MU-MIMO, OFDMA, disabling 2.4Ghz/5Ghz and trying each band separately etc. Doesn't seem to change any behaviors on obeying the congestion rules unfortunately. Almost like the integrated Wireless access point in the device gets to ignore the rules entirely.
Thanks Fraser
Perhaps if we could get a dev to try and replicate this in a lab environment for us. If he can't replicate I would love to know.
Thanks