I've never seen this problem before, but of course it has to happen on the two rides I did during PBP

My Wahoo Roam v1 has syncronised with the Elemnt app, and they both list the correct distance/elevation/etc but the line on the map does not show the full ride. When I upload to Strava, it only includes the section covered by the line on the map, so my 600km to Brest is only showing as 324km. However if I upload the same activity to RidewithGPS, it reports the correct distance and other info (e.g. elevation for the full distance), but only shows the first 324km on the map. The interactive marker on the elevation graph also won't go beyond the ~324km mark.
Presumably there is some corruption in the file, does anyone have any tips on how to fix or diagnose the problem?