Microsoft is famous for breaking DLNA connectivity with OS updates. Since you can't see it in any of your Roku players, the problem is with the computer, not the Roku. Myself, I simply disable the firewall on my home server computers. I'm not concerned with someone on my network attempting to hack into my computers, and they are firewalled from the Internet so no one can get to them that way. I use a DLNA server on my network (Serviio on two different PCs) and they both appear in RMP without any issue. My HDHomeRun network tuner also advertises as a DLNA source, and all of my Rokus can see it as well.
Bottom line: the problem is not with your Roku players, it's the Windows PC.
One more comment: have you made any changes to your home network recently? DLNA only works on networks that use a private IP address range. Most home routers are configured to use an address starting with 192.168.x.x. If your network is not using an IP address range that starts with those two digits, please let us know what the first two numbers are and we can tell you if they are in the right range. If somehow your network has switched to a public IP address range, DLNA will not work, as it's not supposed to be available on public networks.