CalDAV calendar never loads events

Symptoms

When using the Calendar in Roundcube, the cPanel CalDAV calendar shows the "Loading", or "500 Error" and no events are shown.

The Roundcube error log may show errors similar to the following:

[29-Sep-2025 20:50:44 Europe/Rome] PHP Fatal error:  Uncaught Error: Attempt to assign property "_dateonly" on false in /usr/local/cpanel/base/3rdparty/roundcube/plugins/libcalendaring/lib/libcalendaring_recurrence.php:306

[29-Sep-2025 21:00:46 +0200]: <621acf22> PHP Error: iCal data parse error: Invalid MimeDir file. expected: "END:VCALENDAR" got: "END:VEVENT" in /usr/local/cpanel/base/3rdparty/roundcube/plugins/libcalendaring/lib/libcalendaring_vcalendar.php on line 164 (POST /cpsess123456789/3rdparty/roundcube/index.php?_task=mail&_action=refresh)

Description

Certain content of event files (.ics) located within the /home/user/.caldav/address@domain.tld/calendar directory can be corrupted or be incompatible with Roundcube, preventing the events from showing.

We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-49508. Follow this article to receive an email notification when a solution is published in the product. 

Workaround

Locate the ics file(s) within the /home/user/.caldav/address@domain.tld/calendar directory and move them out.