Media files showing 504 error on resource fetch on chrome - .htaccess

Question

On chrome (tried many devices)
My (Angular) web app is sitting on a subdomain and referencing media in a folder in the main domain using https. When using http to access the web app, all media referenced load well but when using https to access the web app, the media don't load and on inspection, media fetch are showing 504 error.
But on Firefox, everything is fine.
Please what could be wrong? Could be the .htaccess configuration or something?
Chrome Developer Tool (Network Tab)
enter image description here
My .htaccess file
`
RewriteEngine on
<FilesMatch "\.(mp4)$">
<IfModule mod_headers.c>
Header set Access-Control-Allow-Origin "*"
Header set Access-Control-Max-Age "3600"
</IfModule>
</FilesMatch>
# RewriteCond %{HTTPS} !on
# RewriteRule (.*) http://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^.*$ /index.html [L,QSA]
</IfModule>
# RewriteRule ^.*$ /index.php [L,QSA]
#for passing HTTP AUTHORIZATION header
CGIPassAuth On
# BEGIN cPanel-generated php ini directives, do not edit
# Manual editing of this file may result in unexpected behavior.
# To make changes to this file, use the cPanel MultiPHP INI Editor (Home >> Software >> MultiPHP INI Editor)
# For more information, read our documentation (https://go.cpanel.net/EA4ModifyINI)
<IfModule php7_module>
php_flag display_errors Off
php_value max_execution_time 30
php_value max_input_time 60
php_value max_input_vars 1000
php_value memory_limit 128M
php_value post_max_size 120M
php_value session.gc_maxlifetime 1440
php_value session.save_path "/var/cpanel/php/sessions/ea-php73"
php_value upload_max_filesize 120M
php_flag zlib.output_compression On
</IfModule>
<IfModule lsapi_module>
php_flag display_errors Off
php_value max_execution_time 30
php_value max_input_time 60
php_value max_input_vars 1000
php_value memory_limit 128M
php_value post_max_size 120M
php_value session.gc_maxlifetime 1440
php_value session.save_path "/var/cpanel/php/sessions/ea-php73"
php_value upload_max_filesize 120M
php_flag zlib.output_compression On
</IfModule>
# END cPanel-generated php ini directives, do not edit
# php -- BEGIN cPanel-generated handler, do not edit
# Set the “ea-php80” package as the default “PHP” programming language.
<IfModule mime_module>
AddHandler application/x-httpd-ea-php80___lsphp .php .php8 .phtml
</IfModule>
# php -- END cPanel-generated handler, do not edit
`
I have searched the internet for solution but clear cut answer