Error 20003 occurs when a completed job cannot be synced because the form (form record) in Salesforce has been deleted. This is very rare and suggests the form was accidentally deleted by a Salesforce administrator as it is not normally allowed.
There are no known recovery method as it is not possible to completely undelete a form once deleted. Any data contained in the affect completed jobs in devices cannot be synced and would be effectively lost.
- Confirm that you are using the correct version of the mobile app.
- Rebuild the form and the job, making sure the data collection task is using a valid form and try again.
- Mobile users should manually delete the completed jobs in their devices, this will flush the invalid jobs to avoid future error messages. (This requires Mobile App version 1.7.2 and up.)