Failed to fetch error when uploading participant's data at the end of the experiment

Hi,

one of my participants got the following error at the end of the experiment.

"Unfortunately we encountered the following error:

  • when uploading participant’s results for experiment …

  • TypeError: Failed to fetch

Try to run the experiment again. If the error persists, contact the experiment designer."

Incomplete data was not saved either. Any idea why?

Thanks!