.tcx file has too few data points won't upload to Strava

I have two suggestions for things you can try

1. Take a tcx file from your Charge 5 and try to upload it. This is just to see if it still works so you know if it’s something that changed on Strava’s end vs something wrong/different with the tcx file from the Charge 6. If you don’t still have your Charge 5, you can download a tcx from an older activity (desktop only) by going to the activity and selecting “export original” from the … menu
2. The tcx format is plain text, so you could try comparing a file from your Charge 5 against one from your Charge 6. See if there’s anything obviously different. Ideally you would do this with two similar activities (same type, duration, etc...)