If you have not already done it, then I suggest shut down your MC server PC, power cycle your router, and then restart your MC server PC. As a further test, if necessary, also power off other network devices.
My Library Server port is set in Options > Media Network > Advanced > TCP Port: 52199.
Two lines down, under "Additional Share Paths", try selecting all three DLNA boxes.
Set Options > Media Network > Add or configure DLNA servers... > DLNA Servers > Generic DLNA
Then check that the same port (52199) is reported as being used in Tree > Services & Plug-ins > Media Network > Server > {your server name} (Library Server).
The 5 LAN Ports used by MC servers are listed and can all be checked per server per the drop down selection box in the same way (which you probably know already). With those three DLNA boxes selected, you should see 5 servers running, each on its own LAN Port.
I don't know how to set the other four LAN Port values - MC's listed values just show up as long as they are available through the firewall (note router port forwarding is not necessary for local network).
If you are using a dual band wi-fi router, is your MC PC server connected on the same band (2.4 GHz or 5 GHz) that you normally used in the past? I don't think the band should affect the LAN Port selection, but I have seen connectivity difficulties in the past when some devices were on different bands.