Hello Mendrik,
We investigated the situation reported by other users who experienced something similar, and the cause turned out to be the Imunify security service.
It is possible that your hosting space is also using Imunify or a similar security solution.
What happens is that this service affects a file called x5engine.php, replacing part of its code with the following warning:

/**
* Note: This file may contain artifacts of previous malicious infection.
* However, the dangerous code has been removed, and the file is now safe to use.
*/

This causes the file to stop functioning correctly.
I recommend that you report this situation to your hosting provider's support team so they can verify whether this is also the case on your hosting account.
If it is, ask them to add x5engine.php to Imunify's ignore list (whitelist) and also submit a report to Imunify indicating that x5engine.php is not a malicious file.
Once the issue has been resolved, the file will be generated correctly again the next time you publish your website.