For what it was worth I would have left the original topic where it was and not created a new topic.
I would have left it alone (ignored) and reported it as a false positive to MBAM, which it clearly is, for a security application to be considered a security.hijack.
That was my first thought - but a google search couldn’t find anyone else reporting the same issue, when I might have expected thousands given the popularity of the products.
As I said, I actually uninstalled avast firewall about three months ago - so perhaps I have an old leftover registry key that didn’t uninstall, and that explains my solitary detection?