Apologies for the delay. The ERA viewer should now display apps updated using the 8.4.0 SDK. If they don't immediately show up try going to Settings > Reset and then Settings > Manage Developers and add your developer ID and Key to re-process the private keys which can take a few minutes to finish.
This method of getting your apps will be changed in the upcoming 8.4.1 SDK. It will instead use your connect credentials which should save a lot of time when loading the ERA viewer.
Garmin is investing so much thinking and then implementing (or in many cases just to announce) things that worked until now and then stop working... Maybe before making ERA unusable for older SDK builds as well by making it require login via the Cloudflare blocked website, it would make sense to fix the developer dashboard first: Can't log in to developer dashboard
I will know more soon, but it will be fixed in 8.4.1 either way as the ERA viewer is getting security updates which involve logging in via connect credentials rather than developer key and id. However, getting a fix for 8.4.0 and earlier ERA viewers is being worked on.
Richard.ConnectIQ is there any ETA for fixing this? Or will the 7z compression and by extension SDK version 8.4.0 and above it be added to the growing list of announced features that never worked from day 1 and are never fixed?