Hello,
It is likely that web shield was not able to connect to the cloudfare server at all or there was an error establishing secure connection; in these cases we have no way how to signal the issue to the browser. These errors should be logged by Avast into syslog. Could you please send us support package (when Avast GUI is active, from menu Help -> Avast Technical Support -> Generate Support Package), ideally just after this error triggers? We will check the logs and try to find out why it does this while the servers are evidently working.
Kind regards,
Ondrej Kolacek