Sitemap not working

@phloo: please provide a url to your xml sitemap.
Thanks

Of course: https://www.wechselpilot.com/sitemaps.xml/

You have an empty line at the beginning of the sitemap.
This guide could help you:
https://www.seopress.org/support/guides/xml-sitemap-blank-page/

We don’t use a cache plugin
We added the debugging and saved all output to debug.log > no error/warnings
We don’t use any of the mentioned plugins

What file creates the output for the sitemaps.xml?

Try to disable plugins one by one and check if the empty line disappears.

Deactivated all other plugins. no change.

What file creates the output for sitemaps.xml?

What file creates the output for sitemaps.xml?

If there is a filter running we can debug.
But we need to know how these files are generated.

The rewrite rules are in /seopress.php line 415 nearly.

Thanks, we could fix it this way.