I have the same problems described above on a new HUb4. I now have another Alexa echo and that is also cutting off. Never had this problem with hub3 and WiFi worked great across whole house. I will spend more time playing around with settings, as previous hub4 went faulty, slowly got worse with intermittent severe slow speeds and cutting off across all devices.
I have noticed that my 2.4G WiFi channel has changed from 11 to 6 (due to neighbours wifi straddling channels on channel 8), but that won’t explain my 5g WiFi which has a free run all on its own.
The Alexa is within 3meters of hub, and speedtest is 500mb/50mb on iPad next to Alexa when Alexa cuts off, so this is an Alexa/VM Hub 4 problem.
