CalDAV Synchronization no longer working with nextcloud

Hello,

since my last update (akonadi 19.08.1 -> 19.08.2) on Oct 22th I am no longer 
able to sync my appointments correctly with my nextcloud server. It used to 
work for quite some time. 

In the server I get messages like this:
> [webdav] Fatal: Sabre\DAV\Exception\BadRequest: A calendar-query REPORT on a
> calendar with a Depth: 0 is undefined. Set Depth to 1 at <<closure>>
 
> 
>  0. /srv/http/nextcloud/nextcloud/3rdparty/sabre/dav/lib/CalDAV/Plugin.php
>  line 250
>  
>     Sabre\CalDAV\Plugin->calendarQueryReport(Sabre\CalDAV\Xml ... l})
>  
>  1. <<closure>>
>  
>     Sabre\CalDAV\Plugin->report("{urn:ietf:param ... y", Sabre\CalDAV\Xml
>     ... l}, "calendars/christian-nextcloud/personal")
>  
>  2.
>  /srv/http/nextcloud/nextcloud/3rdparty/sabre/event/lib/EventEmitterTrait.p
>  hp line 105
>  
>     undefinedundefinedcall_user_func_array([OCA\DAV\CalDAV\Plugin
>     {},"report"], ["{urn:ietf:para ... "])
>  
>  3. /srv/http/nextcloud/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php
>  line 718
>  
>     Sabre\Event\EventEmitter->emit("report", ["{urn:ietf:para ... "])
>  
>  4. <<closure>>
>  
>     Sabre\DAV\CorePlugin->httpReport(Sabre\HTTP\Reque ... "},
>     Sabre\HTTP\Response {})
>  
>  5.
>  /srv/http/nextcloud/nextcloud/3rdparty/sabre/event/lib/EventEmitterTrait.p
>  hp line 105
>  
>     undefinedundefinedcall_user_func_array([Sabre\DAV\CorePlugin
>     {},"httpReport"], [Sabre\HTTP\Requ ... }])
>  
>  6. /srv/http/nextcloud/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php line
>  479
>  
>     Sabre\Event\EventEmitter->emit("method:REPORT", [Sabre\HTTP\Requ ...
>     }])
>  
>  7. /srv/http/nextcloud/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php line
>  254
>  
>     Sabre\DAV\Server->invokeMethod(Sabre\HTTP\Reque ... "},
>     Sabre\HTTP\Response {})
>  
>  8. /srv/http/nextcloud/nextcloud/apps/dav/lib/Server.php line 316
>  
>     Sabre\DAV\Server->exec()
>  
>  9. /srv/http/nextcloud/nextcloud/apps/dav/appinfo/v2/remote.php line 35
>  
>     OCA\DAV\Server->exec()
> 
> 10. /srv/http/nextcloud/nextcloud/remote.php line 163
> 
>     undefinedundefinedrequire_once("/srv/http/nextc ... p")
> 
> 
> REPORT /nextcloud/remote.php/dav/calendars/christian-nextcloud/personal/
> from 134.96.120.223 by christian-nextcloud at 2019-10-24T07:44:23+00:00

Before the update these messages do not appear.

I can modify events (I assume so at least in general) but new events are not 
showing up. Is this a known bug somehow? Or is this the same problem as 
Vojtěch Zeisek asked a few days ago?

Thanks a lot
Christian