We had several reports in the last month or so about the ERA viewer not working for apps submitted with the 8.4.0 SDK (see https://forums.garmin.com/developer/connect-iq/i/bug-reports/bug-server-error-in-era-viewer as an example report). We identified the problem, and have worked with the App Store team to get a fix in place. The fixes have been verified and all apps should appear in ERA viewer with the 8.4.0 SDK as expected now.
Based on our testing, all crash data should be present but it's possible that some crash data may be missing from the past week if your app was updated using the 8.4.0 SDK.