Contacts do not show in web app for all users any more

Describe the bug

I assume since the last version of contacts got installed, the contacts app is empty for all users. DAVx seems to synronize without errors, so I must assume that the contacts are still stored in the DB but the web app cannot read the information.

https://sub.exampel.com/apps/contacts/Alle%20Kontakte

Steps to reproduce

1. Go to Contacts
2. Empty

Expected behavior

I should see my few hundred contacts and groups

Actual behavior

empty contact list, except the circles nothing shows up

Contact version

5.1.0

Operating system

NCP (https://hub.docker.com/r/ownyourbits/nextcloudpi)

PHP engine version

PHP 8.1

Web server

Apache (supported)

Database

MariaDB

Additional info

This is what I see in the docker log when opening the contacts app, even though it makes no sense because everything else works.

2023-02-27 13:22:59 650 [Warning] Aborted connection 650 to db: 'nextcloud' user: 'ncadmin' host: 'localhost' (Got an error reading communication packets)

2023-02-27 13:22:59 651 [Warning] Aborted connection 651 to db: 'nextcloud' user: 'ncadmin' host: 'localhost' (Got an error reading communication packets)

Start by reproducing the empty Contacts web app described in the issue and inspect the reported MariaDB Docker log warnings while opening Contacts. Compare the web app with DAVx synchronization and determine whether contacts and groups are still stored; done means the expected contacts and groups appear for all users without the reported errors.