Also, just to be sure MediaServer is actually running, check its status in the Services applet in Windows.
I just checked my own 2016 R4 media server and it is on port 443. So, for example, I access it via
https://ms1-geo
You will get the certificate error when browsing to the media server, since it is a self-signed certificate, and you have to choose to access the site in spite of the "invalid certificate".
Registry key for the WebConfigServerPort entry is HKEY_LOCAL_MACHINE\SOFTWARE\Interactive Intelligence\MediaServer for 2016 R4
The other possibility would possibly be that HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Interactive Intelligence\MediaServer\WebConfigServerAccessRestrict somehow got set to 1 instead of 0, so check that as well.