That one has nothing as participant in the data file. Did you delete participant from the dialogue box completely? You still need the field called participant, but with not default.
If you arrive from Prolific, you should get the PID as the participant value. If you start at Pavlovia, you should be prompted to enter an id.
I think there is at least one version of PsychoPy with a bug relating to this. What version are you using? Possibly there is still an issue: