Data not saving - Unable to Json decode the value - unexpected UTF-8 BOM

URL of experiment: taskV2 [PsychoPy]
We are losing data of a lot of participants who we see did the task.
at the end of the study we are not getting data saved with the following error:

Any idea what we can do?
Thanks in advance,


I have also been running into this exact same problem for my task. Even though I have turned on “Save incomplete results” on Pavlovia, some participants have ended up with csv files that are blank.

At first I wondered whether it was because my data files were too large (~40 MBs), but I’m not too sure… in a previous run of the same task, the size of the data file led to a different error message, however data still managed to save despite it. In a more recent run, though, it’s been displaying this “unable to JSON decode the value” message and a lot of participant csv files have been blank.

Wonder if anyone has found a solution to this?

Thanks for any leads,

I have the same problem. Have you found any solution for this?