Update:
Unfortunately, I found that Comodo Firewall and/or AV was not happy with HG612stats.
It caused it to run in a strange way where more and more copies of 'HG612_stats.exe' were being run.
Memory was filling up until the PC hung/crashed.
My stats have been going up and down since 03:00am as I investigated the 'Hanging/Crashing' problem.
I cannot understand why but as it runs OK when Comodo is not there I am NOT chasing this as a problem.
I have also now found the error with Avast was caused by a 'missed' configuration page.
Avast optionally scans scripts on all webpages, there is an option to exclude certain addresses which I have never used before.
When I exclude the addresses of the Zyxel router and other routers/AP's I use the GUI problems go away.
Mea Culpa, Mea Culpa, Mea Maxima Culpa .... My Bad !!!Avast is now being reinstalled as it works as I need with minimal impact on using the PC.
Conclusion: Avast does NOT cause problems as originally thought if configured correctly.