CentOS 6.9 (Final)
Product Plesk Onyx 17.5.3
Let’s Encrypt v 2.3.0-190
I have 2 identical Fasthost servers. 1 server is fine and runs Lets Encrypt without a problem. I have just upgraded the new 2nd server to Onyx 17.5.3 (the same version on server 1) but cannot apply Lets Encrypt certificates to any of my domains with only the below source code shown as an error message below (highlighted in red within Plesk).
The domains have had plenty of time to propagate to the new server, so I doubt it is a dns issue.
Internal error502 Bad Gateway