High Sierra contacts disappear immediately after creation I add a contact (Firstname, Lastname, Phone, Email) and save it.

After a few seconds, presumably when macOS tries to sync it to Gmail and/or iCloud, it disappears.

I have a Gmail account and an iCloud account synced, when I add the contact via the Android app, it stays in the Gmail address book and it gets synced into macOS.

At first it seemed to work again, when I disabled the iCloud Account. But: I now try to add a new contact and while typing in the contact details, the editor window simply disappears.

What can I do do make macOS contacts work again?

macOS High Sierra 10.13.2 (17C88)
Solved

Someone in the Apple community gave solved my problem,
 many thanks (https://discussions.apple.com/message/32765319):

Might be a corrupt .plist.

Do a backup, preferably 2 backups on 2 separate drives.

Quit the application.

Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J.  When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder.  Select Library. Then go to Preferences/com.apple.AddressBook.plist.  Move the .plist to your desktop.

Restart the computer, open the application, and test. If it works okay, delete the plist from the desktop.

If the application is the same, return the .plist to where you got it from, overwriting the newer one.