I have an Sony Xperia Z3 Compact with Android 6.0.1 (Sony version, no custom ROM). I use Davdroid to sync to my posteo.de account like described at https://www.davdroid.com/tested-with/posteode/ and https://posteo.de/hilfe/kalender-und-adressbuchabgleich-mit-davdroid-android
Here’s my problem: Whenever someone calls me and afterwards I want create a new contact from this number, then the “Display name” of this contact is set to be the number itself not the name or firstname.
For example: 017xxx calls me. I create a new contact for this number with a name. But the display name is set to be 017xxx and not the name:

Well, obviously it is not very useful to see the number and not the name (seems like the name is not stored with the account info at all).
This only happens so for Davdroid. When storing this number as a new contact as Google contact or on the Telephone, then it works.
Not sure if related but I noticed that for posteo (Davdroid) there are different fields (“phonetic name” etc) when storing the contact:

Whereas for Google contact or the “Contact on telephone” there’s just firstname and lastname (which is fine!):

I had an Samsung S4 Mini with a CyanogenMod ROM (Android 4.4) with the same Davdroid+Posteo setup before and there it was working flawlessly.
Here’s my log: https://paste.fedoraproject.org/paste/XbMtWH~hU~emaSDEnPSTGg