php inserts HEX number of characters before the content

Question

I\'m moving a website to a new server. (Old server had php 5.3.2, the new one has php 5.5.9) Centos, httpd Apache/2.2.26.

I\'ve copied files and it works fine except

Answer 1

Had this problem for serving HTML as well as plain text. EXPLICITLY setting header Transfer-Encoding to "chunked"

header("Transfer-Encoding: chunked");

indeed solved the problem (not sure how reliably though). That Transfer-Encoding header was being added automatically even if i didn't set it - but the problem was still there. Setting the header explicitly in PHP code solved it, but not exactly - see below. Tested using websniffer.cc, PHP 7.4.9, CentOS 7.8

UPDATE: adding the header might confuse some clients. https://securityheaders.com/ failed to connect to the site with this header explicitly set on (regardless of content length)