My app is throwing the above error when I go to re-submit a form which has been edited.
A New Form submit works fine, but when I go back to the gallery, select any previous record, and try to edit it does not submit.

I've tried good ol' google with no luck, some people seem to suggest the error should go after a few tries, but no luck there either. I've tried refreshing the data source etc. and I've also remade the app from scratch and it throws the same error again.
The main error message appears to be:
"message": "Error reading string. Unexpected token: StartObject. Path 'Value', line 2, position 13.\r\nclientRequestId: 5e78521b-d14b-433f-a888-5edb7abfba9c\r\nserviceRequestId: 5e78521b-d14b-433f-a888-5edb7abfba9c"
Is this referring to a specific data card? Can I identify where 'line 2, position 13' is?
I did the full monitoring troubleshoot and it came up with the attached details.
Any help is greatly appreciated, this is the last hurdle on a project which has taken me quite some time!