Hi Sean,
Thank you for your comment. As noted in my OP, configuration is Apache + PHP-CGI.
Compare the results of (curl, or check the browser console):
curl -L -I https://emps.l-c-n.com
curl -L -I https://emps.l-c-n.com/about/
In the second URL, I set those HTTP headers with PHP.
the htaccess files contains the following (which works correctly for other resources: html / JS / CSS / …):
<ifModule mod_headers.c>
Header unset P3P
Header unset ETag
FileETag None
Header always set Strict-Transport-Security "max-age=16070400"
Header always set Referrer-Policy "strict-origin-when-cross-origin"
Header always set X-XSS-Protection "1; mode=block"
Header always set X-Frame-Options "DENY"
Header always set X-Content-Type-Options "nosniff"
Header set Content-Security-Policy " default-src 'self'; font-src 'self'; img-src 'self' data: * https://*; media-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'self' https:"
Header always set Permissions-Policy: accelerometer=(),ambient-light-sensor=(),autoplay=(),battery=(),camera=(),display-capture=(),fullscreen=(self),geolocation=(),gyroscope=(),interest-cohort=(),magnetometer=(),microphone=(),midi=(),payment=(),picture-in-picture=(),screen-wake-lock=()
I will email support next for the gzip part.
Thank you again