What to do when Google only syncs some of your contacts

When some of your Google contacts are no longer synchronized with your e-mail client or mobile phone, those contacts are not in a group "My Contacts". Google only syncs contacts in that group.

In order to fix this:

• Open Google Contacts Show archive.org snapshot
• Select all contacts (there's a link)
• Press "Move to My Contacts"

Note that when you are using Mozilla Thunderbird with the Google Contacts add-on Show archive.org snapshot , Thunderbird won't add new contacts into the "My Contacts" group by default.

I also suspect that the mentioned Thunderbird addon has a feature where it randomly moves contacts in and out of that group.