Emails missing since import from version 6

All my emails missing since upgrade to version 7. The only ones I have are from when I installed eM client 6 in April and the ones from the last few days from the server.
I’ve tried to import from version 6 again and still no change.
I do have a Windows backup using 3rd party backup software and wondered if I can restore some folders but I do not know what folders I need and where they are, partcularly the difference between v6 and v7 folders.
Any help would be most appreaciated