Asked to return after completion: Tasks ran out while connecting to the study

I just did a certain study with dynamic rewards, spent a little over an hour on it. Clicked on the button to finish it, received the "Current session is complete, We received your data. No further action is required" page. Only to be immediately greeted by the message:

"You have been asked to return your submission for "[redacted]" for the following reason(s):

• Tasks ran out while connecting to the study."

Now, I had those before but always at the beginning of a study. Got a spot, tried to start the study: "Tasks ran out while connecting to the study"

Alright, fair enough I'll return it. But this time it let me spend over an our on it with no issues, only to ask for a return at the end? Does anybody have any experience with this? It would hurt to return it, but at the same time I don't want to slay the goose that lays the golden eggs.

I contacted the researcher, but I have my doubts I'll ever here from them.

Thanks for your input. :)