For a couple of days now whenever I receive a link to a live activity at livetrack.garmin.com all I see is a blank screen (tested in current Chrome, Firefox, and Edge browsers).
Checking the browsers' error consoles and network activity it seems that the main.js is incomplete. This can be confirmed by opening the link to that file directly. It just ends (always at the same spot).
This is the file that is incomplete: https://livetrack.garmin.com/js/main.js?bust=1.107
The received main.js is attached as a zip file since you don't seem to allow attaching js or txt files.