I have been rebooting them whenever there is down time, which does not currently seem to be too often! However at least once a week. I tried resetting the Hub3 to factory defaults a couple of weeks ago and it went back to the 302 firmware. It updated automatically to 304 again at some point after. I though the reset would get me back to the stability of last summer, but the last week has seen at least once dropout per day.
Originally I had my work computer on a BT powerline to the back of the hub as well, which I ditched to go fully wifi. I thought the powerline might be interfering, but it has made no difference.
Also tried router mode with wifi switched off, but made no difference.
completely stumped at moment...