I had that exact same issue, I believe quite a lot if people have. The issue seems fixed on my device since installing beta 3. What seems to be the issue is the system information / diagnostic that the app is gathering, it cannot seem to sent it sometimes.
My workaround before it seems to fix it's self was to submit as normal and if the thing sat in the outbox and after a while said "failed to send" i would edit the report and just remove the attached system diag file, confirm I would like to sent without and then it would go almost instantly.
Now I know that's not idea and Apple need as much detail as possible - I am of the opinion that they should at least hear the feedback, or as much of it as possible - even if that means not getting the whole picture.