Did you import any modules? You need to go to each module, especially JSON and aggregator modules, and click Save. This should resolve any missing data structures by clearing that field, since data structures cannot be imported.
Hope this helps! Let me know if there are any further questions or issues.
— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!