Hello nigelrmscott,
if this issue persist can I ask you to collect and send me application logs? Specifically, I need this file "C:\ProgramData\AVAST Software\Avast\log\AvastUI.log". You can attach the file to your message here on our forum.
Also, I am gonna need Avast application version you have installed (Settings > About Avast) and which OS you are using.
Thank you
Manas from
Avast UI team