Categories (AKA Groups or Tags) not synced through Carddav


Connecting a CardDAV client to Nextcloud 16 Contacts suffers from big problems related to CATEGORY field not being synced correctly or reliably. It seems to me that it used to work in v14 or v15.

I tried two different CardDAV clients (eMClient and the Busycal) without success. The results are somewhat random : sometimes it syncs in one direction only, sometimes both, sometimes none.

Anybody has had the same problems ? How would I debug this ?

Thanks for sharing your toughs.