recreating the the contacts file solved the problem.
Hello, I’ve just installed Davx.
I want to synchronize from my smartphone (with many contacts) to nextcloud (which is empty)
I installed nextcloud client , then Davx.
I ask for synchronization of CardDav. I see synchronization is being processed … but there is nothing transferered to nextcloud!
I have a Samsung ; the “maximum mode” for battery is not activated.
Sorry for my unuseful post