Just wait. It takes a little time for the DNSSEC change to take effect. Don’t keep enabling/disabling Universal SSL or you may hit the rate limit of the CA which will delay the certificate further.
This is not a live chat. Help is often given by users in their own free time, or while working on their day work. Responses may take time or be given by other users.
The 504 grapical error page from Cloudflare means your origin server is returning a 504 to Cloudflare, which it is as below. You will need to fix the problem there. Pause Cloudflare first, fix your origin server (which is working with http but not https), and when it is working properly you can re-enable it again.