Error uploading participant's results

URL of experiment:

Description of the problem: I started collecting data recently and out of the 4 participants I tested, 2 of them experienced this error right at the end of the experiment.

“Unfortunately we encountered the following error: when uploading participant’s results for the experiment” and “when flushing participant’s logs for the experiment, when uploading participant’s log for the experiment”.

This error occurred at the end of day 2 of the 3 day experiment. I did not encounter this error before when collecting data and the only changes I have made is that participant’s are now redirected to a different questionnaire on qualtrics for each day, so I have made 3 different experiments one for each day depending on the questionnaire they need to complete. After these 2 participant’s got this error they then cleared their cashe and redid the experiment and after doing this they didn’t get the error. I have also heard that it may have been because of a drop in internet connection.

I have seen a lot of people with this error and wondered if anyone has found exactly why this occurs yet and how it can be prevented?