Mautic 6.x – Forms preview and submit return 500 with no logs generated

Product Support
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1

Your software
My Mautic version is:v6.0.7
My PHP version is: 8.3.28
My Database type and version is: 10.6.24-MariaDB-ubu2204

Your problem
My problem is: Mautic 6.x – Forms preview and submit return 500 with no logs generated

Hi,
I’m running Mautic 6.x in Docker behind Cloudflare (HTTPS) and I’m facing a persistent 500 Internal Server Error when:

  • previewing forms (/s/forms/preview/{id})

  • submitting forms (both embedded and UI preview)

The issue occurs before form validation and independently of the fields used.

Key details:

  • No log file is created in the configured log directory (var/logs)

  • prod.log is not generated at all

  • The path configured in System Settings → Path to the log directory exists (or is created) and is writable

  • Cache has been cleared

This looks like a Symfony session / CSRF / filesystem issue rather than a form configuration problem.

Questions:

  1. In Mautic 6 Docker deployments, what is the expected value and location for:

    • kernel.logs_dir

    • PHP session.save_path

  2. Are there known issues in Mautic 6 where:

    • invalid or unwritable kernel.logs_dir

    • or session storage problems
      cause silent 500 errors with no logs, especially on form preview/submit?

  3. Is there a recommended configuration for:

    • sessions

    • CSRF

    • filesystem permissions
      when running behind Cloudflare / reverse proxy?

Any guidance on the correct logging and session setup for Mautic 6 in Docker would be appreciated.

Thanks
Chapa