I’ve been getting this error message for some time now.
[Google Contacts]Sincronização de pasta ‘email@example.com/Contacts’ falhou devido ao seguinte erro: SQLite Error 19: ‘constraint failed’.
How to get around this problem (very old and persistent)?
Right-click on the Gmail Contacts folder and choose Properties > Repair > Repair.
Initially the contacts will disappear, but after the next sync, or a restart of eM Client, they will be there again.
Following the instructions, the problem appears to have been resolved. I’ll wait a few more days and confirm if the problem has been resolved.