Why does the browser display the original html code of the site?

Question

HTML

Good afternoon.
I ran into one mysterious problem: on the site from time to time, when you try to load a page, the html code is displayed, there are no errors on the server. It only helps clear cookies.
Where to dig in this situation?
Thank you.

Answer 1

Check Content-Typethe header in the server response.

Answer 2

Is this a clear browser issue, or are you somehow serving a page with mimetype text/plain instead of text/html somewhere?