When I've done mine in GoSpotCheck, there is an indicator telling me how many of the required questions I've answered it says something like:
2 required 1 Optional
Before I click start mission.
After hitting start mission it states:
0/2 required 0/1 optional
Once I click site verified that number increases to 0/4 required.
When you are trying to submit your report, are you seeing 4/4 required (for my example) or 3/4 which would mean you are missing a question.
Also, do you have a data plan or wi-fi when you are trying to submit the report?
Just some ideas.