I've found posts in this forum regarding the error message "Invalid argument supplied for foreach() ...." when trying to access the form data, and one of the solutions offered was to run the Meta Recovery tool. However, that has not worked in my case.
I was unable to do a wordpress export/import because of the sheer volume of data in the web site - and so did a SQL export and ran the table creation via phpMyAdmin for the migrated site. In addition to not being able to see the form submission data, we cannot export any data. I'm not entirely sure which table I should look at, but one of the tables with form data (wp_contactform_submit_data) looks intact - Is there any way to retrieve the data for my client?