Server error 500 | ErrorException: stream_get_contents(): file created in the system's temporary directory

[codiflow]

Baikal version: 0.10.1

Expected behaviour:
The error message on server side helps me finding the issue with the affected calendar entry.

Current behaviour:
I'm totally lost how I should debug this issue as the error message (ErrorException: stream_get_contents(): file created in the system's temporary directory in /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/CalDAV/Plugin.php:787) is not helpful for me.

The whole story:
I'm using Baikal since years now and around 20-30 people are working with the calendar on a daily basis. So we have a bunch of older entries which have a recurring rule in it and are there for a longer time.

Since many years it happens from time to time (every 2-5 months, currently around every 2-4 weeks) that editing such an entry fails on client side (giving me server 500) and the client is stuck since then. It cannot sync the changed entry to the server because of the error 500 and with apps like DAVx5 it is also not able to pull updated entries from the server. We absolutely have NO clue until now what is the root cause. It happens to Android devices and to iOS devices of any kind.

The only solution is to either reconfigure the client (delete everything and do a clean pull from the server) or to delete the entry causing the issue on the affected client. As we don't have logs identifying the device (apart from IP address and device type / version) this is rather cumbersome.

I try to tear down this issue over and over again each time it happens but there seems to be no clear trail what is causing this issue. At first there were some issues which matched this issue but this is not the case anymore.

This time the error message is different and I'm absolutely lost interpreting what could be the issue here as the calendar itself is working fine (so no general PUT upload issue): ErrorException: stream_get_contents(): file created in the system's temporary directory in /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/CalDAV/Plugin.php:787

The full log:

mod_fcgid: stderr: ErrorException: stream_get_contents(): file created in the system's temporary directory in /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/CalDAV/Plugin.php:787
mod_fcgid: stderr: Stack trace:
mod_fcgid: stderr: #0 [internal function]: Baikal\\Framework::exception_error_handler()
mod_fcgid: stderr: #1 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/CalDAV/Plugin.php(787): stream_get_contents()
mod_fcgid: stderr: #2 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/CalDAV/Plugin.php(733): Sabre\\CalDAV\\Plugin->validateICalendar()
mod_fcgid: stderr: #3 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\\CalDAV\\Plugin->beforeWriteContent()
mod_fcgid: stderr: #4 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/DAV/Server.php(1133): Sabre\\DAV\\Server->emit()
mod_fcgid: stderr: #5 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/DAV/CorePlugin.php(492): Sabre\\DAV\\Server->updateFile()
mod_fcgid: stderr: #6 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/event/lib/WildcardEmitterTrait.php(89): Sabre\\DAV\\CorePlugin->httpPut()
mod_fcgid: stderr: #7 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/DAV/Server.php(472): Sabre\\DAV\\Server->emit()
mod_fcgid: stderr: #8 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/DAV/Server.php(253): Sabre\\DAV\\Server->invokeMethod()
mod_fcgid: stderr: #9 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/vendor/sabre/dav/lib/DAV/Server.php(321): Sabre\\DAV\\Server->start()
mod_fcgid: stderr: #10 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/Core/Frameworks/Baikal/Core/Server.php(118): Sabre\\DAV\\Server->exec()
mod_fcgid: stderr: #11 /var/www/vhosts/<REDACTED-HOSTNAME>/httpdocs/baikal/html/dav.php(69): Baikal\\Core\\Server->start()
mod_fcgid: stderr: #12 {main} 

Do you have any clue what I could check to find the cause for this?

Steps to reproduce:
Not directly reproducible but currently happening.