Inherited theme causes empty first line in all documents

I am using a theme inherited from Antimatter. Once this theme is activated all generated pages start with an empty line. (I added line numbers to code below for better explanation)

2 <!DOCTYPE html>
3 <html lang="de">
4 <head>
5 ...

This behavior is annoying in combination with sitemap plugin as it leads to a faulty XML document.

If i switch to plain Antimatter the empty line is gone.
Any idea how I can get rid of this empty line in my inherited theme?

I am unable to replicate this problem. Please post a zip of your child theme to test.

Thanks for your quick response. Here is the child theme.

I did some further testing and have created a simplified version of the website, i.e. child theme reduced to essentials, web pages just copied from antimatter example, most of the plugins deinstalled. Updates of today installed. Issue is still there. I have posted a zip of the simplified web site under the same link than the full child theme.

I opened your theme’s main php file and just saved, and it was fixed. The issue is you have some white space after the closing ?> tag.

I have my editor configured to strip white space, you might want to do the same.

Thank you very much for your great support. You helped me a lot. Issue is fixed. You made my day.