a_4_{s_7__headers_ page wants to download

Hello ladies and gents

I have an issue I’m not able to fix. When a visitor wants to open the homepage, the site wants to download a file called a_4_{s_7__headers_ (file is empty) but after you refresh/reload the page, it loads normally.

So far I tried to replace .htaccess file with a new one (it helped with a similar problem on some other site). I also tried to deactivate all plugins and that also didn’t help. I don’t have any other idea what else to try.

All plugins and wp are up to date.

Thank you for your help.

The page I need help with: [log in to see the link]