Similar for me. Heard someone on radio say delete the app and reinstall which I did and it worked very easily. But updating the app version is smarter.I found that the key is to update the version of the Service Vic app. Go into version History and click on 1.14.0 and it works. Some of my friends found that even when there was no trigger to get that latest version by doing that it means you get the icon to link the certificate
Colleague said the app has a feature to capture your certificate to show separately to a venue checkin but haven't tried it.