Symptoms
Your server is running LiteSpeed, and you have an .html file that contains both PHP and SSI (Server-Side Include) code. When you access the file in a Web browser, you observe that only either the PHP code is run or the SSI code is parsed, but not both.
Description
This is a limitation of LiteSpeed, which is unable to parse PHP in .html and SSI simultaneously without manual modifications.
Workaround
Switch the server to use Apache, which can handle parsing both PHP and SSI in the same .html file.