I noticed this too. The last successful import into Google Earth was on March 10. All activities from March 11 on do not have a track after exporting to Google Earth.
I have a workaround that I've been using until Garmin can fix this:
- Export the activity as GPX
- Open the GPX file with TCX Converter
- Save the GPX file as a KML file
- Open the new KML file in Google Earth
Title says it all really. Doesn't seem to have been working for the past month or so. .kml file is exported but when opened in Google Earth only the start and finish shows but no route. It's a real pain as I use it to plot my orienteering runs. I mark each control as a Lap and then use Google Earth to visualise my route. Can't use Garmin Connect itself as although the route is plotted, only a limited number of laps show up. Can't quite figure out what's wrong with the file that's generated, but like others have commented with gpx and tcx exports, no altitude data is present.
Thank you for contacting Garmin International.
We are aware of the issue, and it is currently being looked at. I am sorry but so far, there isn't a date they will have an answer for you. Our engineers are working hard to get the issue fixed so our customers can once again enjoy the export of activities with Google Earth track. I do apologize for the inconvenience this has caused you.
Please let us know if you need further assistance.
This was reported on this forum last month and the problem was relayed to Garmin support. See workaround below.