Contacts not showing up in contacts app

[jankkm]

Since upgrading to nextcloud from owncloud 8.x I have problem with the contacts app. It is running on a shared hosting. I have 462 contacts in my address book synced between multiple Apple devices which still works fine but the contacts web app just shows "No contacts in here". If I remove about 20 contacts it works and it does not matter which contacts I remove so this is not about a faulty contact. This was not the case on owncloud 8.x

Any idea what the issue could be? Or how to get any more information? There is nothing interesting in the log file.