Which specific errors?

Actually it didn't list a specific error which makes it harder to tell what went wrong. As you can see from the first screenshot it doesn't really give much info other than not importing all the addresses. Not why it could not.

The second screenshot shows that it created a duplicate "Collected Addresses" book instead of importing it directly into the one that is already there. The same issue occurs when importing the "Personal Address" book as well.

Not sure why it is not working as it should. I used the first option to export, CSVs. Is there a better choice?

Use the LDIF format. After import, you can simply drag all addresses from the duplicate books to the respective books then delete the duplicate.

That did the trick...Thanks!

Do you know why it does not automatically import them into the default Personal and Collected Address Books?

I have no idea, but I think it's a safeguard in a way. Personally, I prefer this approach so that if things don't go right, your existing books do not get botched in the process.

I guess that makes sense. I also noticed that you can delete these "new" address books (which have a dot preceding the name when deleting) but not the default ones. Anyway thanks again for the tips on how to make it work.

This is really a headache. In Thunderbird 68, I can do a perfect import of addresses from my Google address book, using the vCard file (.vcf) format. I have a large address book with over 5220 contacts contacts, and in Thunderbird 68, this import works perfectly. I reinstalled TB 68, but then my system updated automatically to TB 78, without asking me. And now I have the same problem again. LDIF /CSV import creates a complete mess, and in TB 78 (Windows 10, 64 bit) I can only import 590 of my addresses. Please fix the bug so I can do a proper import of my Google address book. Furthermore, in the import in TB 78, the Norwegian letters are twisted. I do not want TB78 when it is like this.