Workout map route colors explanations:
Yellow is the average pace.
Green is the fastest pace.
Red and orange are the slowest paces.
All sections are based on averages for that section and length of time to complete.
If there are grey dots on the route this is a weak or non existent GPS signal.
The dots are where the watch is filling in the gaps.
The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:
How to restart your Apple Watch - Apple Support
Restart your iPhone - Apple Support
If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup. This deletes all temp and corrupted files and re-indexes the file system.
Unpair and erase your Apple Watch - Apple Support
Set up your Apple Watch - Apple Support