After trying various things, it works again after I deleted the drop-down menu answer option from the form. It somehow got stuck on the drop-down, which disabled the data to upload from that point onward.
A bit strange, since the forms have worked a long time without any issues concerning this answer option.
I don’t whether this is something common, or whether there is some kind of alternative way of still using drop-downs in the forms?
I look forward to your reply.
But for now is kinda working again I guess.