User submitted content not working – please help this newbie

Have you tried:

– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the default theme to rule out any theme-specific problems.

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

– re-uploading all files & folders – except the wp-content folder and wp-config.php & root .htaccess files – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.

I pressed f12 and got this in webdevelopers tools

ixed Content: The page at ‘https://jetpack.wordpress.com/jetpack-comment/’ was loaded over a secure connection, but contains a form which targets an insecure endpoint ‘https://www.madaboutkids.co.uk/wp-comments-post.php?for=jetpack’. This endpoint should be made available over a secure connection.
jetpack.wordpress.com/jetpack-comment/:92 Mixed Content: The page at ‘https://jetpack.wordpress.com/jetpack-comment/’ was loaded over a secure connection, but contains a form which targets an insecure endpoint ‘https://www.madaboutkids.co.uk/wp-comments-post.php?for=jetpack’. This endpoint should be made available over a secure connection.
https://www.madaboutkids.co.uk/wp-comments-post.php?for=jetpack Failed to load resource: net::ERR_EMPTY_RESPONSE

I have no idea what this means or how to fix it. Can you shed some light?