Thanks to both the above posters.

DavidR I have checked the active window title bar font size, it is set at 8, so no problem there.

iroc9555 icon image stays as per my screenshot after rebooting.

A bit strange, but not a deal breaker, maybe one day it will return to normal in the same way it went low resolution :wink: Thanks again.
PS all other taskbar icons are normal, ie as they always have been, only Avast is different.