Please go to your Cloudflare Dashboard > Security > Events and try to find which security feature of Cloudflare is blocking access to xmlrpc.php, then post pack here.
@cbrandt thanks for your reply, I checked ‘Cloudflare Dashboard > Security > Events’ but I don’t see any event related to blocking access to xmlrpc.php. Is there any other setting I should check?
Actually, this issue seemed to be related to one of the plugins (Really Simple SSL) causing an issue with accessing xmlrpc.php. After disabling it my website can sync to the Jetpack and the Wordpress app again.