Contacts gone and full resync everytime

[Thrandu]

Hello everyone,

i dont have an idea what the issue is.
Since 2 days i see on my Phone that my Contacts are gone and will "re-created" everytime.
If i go to my Accounts on the Phone, Exchange Nextcloud Integration and Resync contacts, then they are back, if i click "resync now" then all contacts are gone and will be full downloaded again, why?
Additionaly it looks like a Contact is gone now forever.
I didnt change anything on the server, it happents without any changes on phone or server.
I try to reboot the server, "reinstall" mail-in-a-box, looks for z-push logs, remove my device and add it again, nothing fix this issue.
Normally if i "resync", the contacts should be still there and remove/add the changes and not remove everything?
What did help to find maybe the issue?

If i check the z-push error logs i see a lot of
Mobile loop detected! Messages sent to the mobile will be restricted to 1 items in order to identify the conflict
Messages if i sync
This is happents sometimes:
SyncObject->Check(): object from type SyncMail: parameter 'to' contains an invalid email address 'undisclosed-recipients:;'. Address is removed.

And i see a lot of
BackendCardDAV->GetGALSearchResults : Error in search Woops, something's gone wrong! The CardDAV server returned the http status code 405.

What else can i check?

/edit
I did switch now to DAVx App and now everything is stable.
So for me it looks like something is broken with Z-Push with the current packages (November 2025) or Google did something weird with System Apps and Exchange Sync.