Hi Olaf Bartelt,
Thank you for contacting Syncfusion Support.
We have already found and fixed the issue “Appointments not showing in DayView anymore”. The issue fix has included in our latest Weekly NuGet release. So, can you please upgrade to our current version (18.1.0.48) which is available for download (nuget.org).
We hope this helps. Kindly revert us if you have any concern.
Regards,
Muniappan S.