I have the Galaxy Watch Active2 and have been using it for my runs. I know my distances pretty well and started to notice that the watch was recording a much shorter distance than I knew I was running. I decided to test out the watch on a controlled run and discovered this in my map. I always start and end my run in the same place, my house. However, the map is showing that my run didn't start until I got around the corner from my home. What gives?
Are you using the auto detect workout on your watch or are you starting the workout yourself?
You need to have the watch resolve your location before it can log your route. My Galaxy Watch is rather slow and inconsistent in acquireing a GPS lock when using the watch Samsung Health app. Try to have it fix your position with as clear view of the sky as possible before you start (a steady green location icon). (As a side note, the auto detect never tries to acquire the position to log on the map on my watch. Only a manual start does that.)