Reserved credits, no data saved

URL of experiment: Conversation in Japanese [PsychoPy]

Description of the problem:

Hello, I have seen several posts about this problem, but with no clear solution, and so I am taking another shot here.
I am “piloting” (in running mode) my study to make sure that I’ve dealt with any problems before distributing my study to potential participants.

I allotted three credits to my experiment, and two of my acquaintances took my study last night. I am certain that they did not quit in the middle, since at least one of them has helped me with this before.
I am encountering a similar issue with other people, in that two credits now appear as “reserved,” and no data was saved (I have it set so that incomplete results are not saved).
My study is set so that once participants see the final “thank you” message in my final routine, they click their mouse and the routine ends. Then I assume that they close their browser window or tab. The esc key was not enabled.
This experiment was put together on PsychoPy Builder, if that is useful information.

What can I do to prevent this sort of issue from happening in the future? Thank you for your time reading this!