trilogy6202
I don't use Simple Contacts, but I just tried it out to see if I have the same problem (I also sync with Nextcloud using Davx5). No issues for me here. I created new contacts, updated them, and deleted them on both my phone and on Nextcloud, everything synced as expected.
Have you odd errors thrown by DAVx5? Maybe make sure the app is allowed to post notifications in Settings > Apps > All apps > DAVx5 > Notifications, then enable all. Try syncing again and maybe you'll get an error message? I had a sync issue not long ago where DAVx5 didn't like a field or something that I was using with a contact.