Resolve myriad of JSON processing errors

[tameTNT]

These seem to happen all the time during normal operation with lots of judges but I have no idea what causes them and in many cases they can be resolved simply by logging out and back in or clearing cookies or changing browsers but they manifest at different times when submitting projects, getting a next project etc. For some users, the above worked, but for others, their account was completely bricked (Karl) and they had to start afresh.
These may be separate issues with the same error message so we really need to first separate out these errors and understand what's even going wrong.

[tameTNT]

Believed to be separate from token issues?

[tameTNT]

Best approach here is probably to first implement proper error messages in different parts corresponding to which field in the response/request actually caused an issue.