I have been having same issue. 2G is fine, 5G locks up. I switched the channel to 52+56, this worked really well for a good few days and I stopped getting outages but unfortunately Amazon Echo and Fire TV stick don't seem to work with this channel and I had to make them use 2G. There are lots of reports that Fire TV only works with the lower channels.
I wondered if it was just an issue with using auto channel, so I tried all four manually, 36+40, 40+36, 44+48 & 48+44 but still get outages. I doubt its just the interference from the neighbours otherwise the problem would not go away when I reboot it. I can only assume the Superhub locks up the 5Gb somehow due to the interference and doesn't unlock until its rebooted.
Does anyone know if Superhub 3 has same issue? I would ask to switch but have seen to many other issues with Superhub 3.