Hi Danie,
One option you might try if you are able is to back up the project, delete the old project, and then re-import it back into the newly created project that you have. It could be that after the upgrade there is some code that was corrupted so this could refresh it.
However, if you are already have a call with SAP this might not be the best option. You can try it after the call if recommended by SAP.
Are you able to reproduce this same error in a different environment? For example if you can create a duplicate project in a different environment, then export the project that is having the issue and then import it to the same project, but on a different environment.
This might show if this error re-appears in regardless of which environment you are in.
In either case good luck.