I happened to look up a race I did last year on Garmin Connect. It seemed to pause for a few seconds before showing the map, which shows a straight line instead of the actual route. Further, the heart rate and speed charts are missing. Lap data is fine.
Then I checked Strava. Everything looks fine. Strava, of course, gets its data from Garmin Connect and I'm pretty sure the data on GC looked fine last Fall.
I even tried dumping the FIT file from Garmin Connect. The dump was fine but when I tried to reload the data, GC gave an error and refused. So, it looks like my data, which was uploaded clean and stored by Garmin Connect was corrupted at some point over the last few months. Very frustrating. I haven't tried for a while, but the last time I tried to download data from Strava, much detail was lost. I guess I'm going to have to start backing up my data locally. Unfortunately, I deleted this activity from the watch some time ago.