Apple Watch Workout routes cut off

Many times when I do a longer run or work with a Series 3 (90+ minutes), a good chunk of the first half of the route is missing.

For example, if I do a 20km run, the map shows that the starting point was km 6. Distance and time information is accurate, but the map isn't.

This has been happening regularly since I updated to iOS 14 and WatchOS 7. Typical solutions like calibration, unpair/pair, etc. don't help.