I have recently upgraded my MDS server from Mojave to Catalina and after the upgrade the web server was not able to open. The port looks to be in listening mode, I confirmed it by using the sudo lsof command with the dedicated port for MDS. I have completely uninstalled and reinstalled the mds application as well. One note is that this server is also hosting OSX Mac app as well for MDM, which has its own set of ports.
Please let me know where I should be troubleshooting now.