The Tableau Desktop logs will have a line specifying what JSON field caused the error. For example:
LogError: Error reading JSON payload with expression 'files.lastModifyingUser.displayName'. Field 'lastModifyingUser'. JSON Error: get_value< Object > called on null Value
The JSON can be connected in Tableau Desktop (copy and paste in the Data menu) to find the documents which are causing the error.
Once the specific documents are known, they can be removed from the Google Drive, or you may replace nulls with actual values.
The sheets can still be searched for in the search box even if the list is not populated. If a specific sheet's name is know enter it into the search box and a connection can be made.