I have this error using
Nextcloud 13.0.4. I’m accessing a contact both from
Evolution 3.28.2 and
Davdroid 126.96.36.199-ose (happens since 1.11 IIRC). Apparently this would be because
Evolution inserted in the VCard a
Davdroid didn’t understand, and instead of replacing it
Davdroid adds its own one, which makes the server unhappy.
This bug has already been reported and fixed a while back, but it recently resurfaced.
(Slightly edited) debug log: 0_1529417055399_debug.txt