Eureka. I suspect the problem and solution may be unique to myself, but just in case.
I use Firebox as my web browser, and DuckDuckGo as my search engine. I had added the following Extension to Firefox -
It has been there for some time and this is the first time to my knowledge it has caused any issue. You can exclude sites, so simple to allow access to the Charger web page either direct using the IP address, or via the URL used by the Device List.
I hadn’t tried to access the Charger web page since April/ May this year. There was no problem then. Two changes since the Spring 1)The Charger firmware update 2) The DuckDuckGo extension had an update late October, so no clear evidence as to which update caused the issue.
Perhaps if a clever person from Victron reads this they can confirm/check it wasn’t the Charger firmware. Either way problem solved for me. Yippee!
David