No luck. I went into :-
■ Settings/Developer_Options/Running_Services and stopped both Avast entries
■ Settings/Apps and did a force stop
Then into Settings/Accessibility/Installed_Services (Avast was already OFF) then into the Avast entry and switched it ON - then I got a popup about needing to grant the Full Access permission, which I granted.
The Avast/Settings/Protection list showed Web Shield to be off, but when I clicked on the slider I was back in the same loop as before.