At the log I’m getting lines like
[error] Received VCard with not exactly one VCARD, ignoring b1c5e8a83b8da48fe0dfc6d654307ad494b1b12f
The VCard that it received is
BEGIN:VCARD EMAIL:email@example.com FN:Foo Bar N:Bar;Foo UID:b1c5e8a83b8da48fe0dfc6d654307ad494b1b12f X-CALYPSO-NAME:b1c5e8a83b8da48fe0dfc6d654307ad494b1b12f END:VCARD
If I have only one contact in my agenda DAVdroid sync it without problem but not with two or more contacts.