It appears I'm also suffering this issue. To be honest, I'd given up on 5ghz some time last year. It just wouldn't stay connected for any reasonable amount of time, on any device. The only reason I've recently revisited it is to use xcloud game streaming, which apparently works much better over 5ghz.
1. Brief description of the problem, and how is masquerades itself. What are the symptoms? How frequently does it happen?
Either can't connect to the 5ghz connection (says connected without internet on Android devices, for example) or, if I can connect, will lose that connection seemingly at random.
2. Do the devices having problems appear to be connected or associated with the hub? Is the hub status indicator normal/blue when the problem occurs?
The hub is working fine
3. Do you have the 2.4GHz and 5GHz channels merged (default setting) or split (different wireless network names)? If the networks are named differently, does the problem only affect the 5GHz network?
The two channels are split, with different names. 2.4GHz works just fine.
4. Once the problem occurs is it persistent? Do you have any devices wired to the router and does the problem affect them at the same time?
Once a 5GHz connection is lost, it won't reconnect without restarting the router. I have a couple of wired devices that are unaffected.
5.Are you able to reproduce the problem reliably? Do you think you have a way of triggering it? [for example waking a specific device from power save mode]
No
6. Is the problem always resolved by rebooting the hub? If so, how long does it take before problems recur?
Usually a reboot will fix the issue, but it will always return. No pattern to how often it happens.
7. If specific devices are always impacted when problems occur, please provide details of which devices are impacted and which aren't i.e. manufacturer, model, variant and operating system version.
Have only tried 5GHz with a Samsung Galaxy A40, and two Amazon Fire Sticks.
8. Have the devices experiencing problems recently received any patches that might correspond with the time the issue first occurred?
No.
9. Please provide a description of your home network setup and all devices in use including whether or not you're using any additional switches, Powerline adapters or wireless access points.
Just using the router, wired to a PC and Xbox One. Then wireless (2.4GHz!) to a few phones and tablets, Fire Sticks, couple of other games consoles and a printer.
