SOLVED. Ended up being Command GUI, added by someone secretly

We've been using Gringott's with Vault and Jobs for a week with no loss of function, but now Jobs is not paying out for any action. Examination of the logs finds this error:

https://pastebin.com/EVVx1nAT

Any clue as to what is happening would be appreciated.

If you have found the solution please close the issue! :)