@Efejota said:
My guess is that the watch at some point stops using GPS to save battery in critical conditions
I don’t think this is it. He said he still had 18% left at the end of the activity. On older firmware, things used to shut down more aggressively, but that was some time ago. The first low battery warning does pop-up at 20%, but does not affect any settings. IIRC, things don’t start to shut down now until around the 5% range.
Although, I suppose things could be different for such a large activity. Perhaps the 9PP was running out of memory at that stage? The fact that the activity distance is longer than the GPX distance does suggest that it shifted into Tour mode (GPS logged every 30 minutes) for the final 1.5km, logging one final GPS point at the end of the activity, but not connecting it to the GPX trace.
I seem to recall some other folks having issue uploading extra long activities to SA, but can’t recall if it was watch model specific.