Got a similar issue. Got an AX86U and all my 2.4GHz devices work fine on _4. Upgrade to _6 and most of them fail to connect or drop connection continually/very slow throughput/can't stream. Restarted etc etc.My devices don't like the firmware that are connected to the AC68U router on 2.4Ghz band. Every hour on the hour, while streaming a movie, tv show; a device will stop streaming and has no internet connection for about 30 sec. Even though a device is still connected to a router via wifi. Tried different channels and still no joy.
Nothing odd in the logs.
Rolled back to _4 and no issues. So I respectfully disagree that it's something with my setup.