The most likely cause is that Windows blew away the exceptions for Roon and RAATserver on the client. Try turning off the Firewall on the client PC and see if the audio endpoints appear.
Since your Core is Windows, you might also verify that the core Firewall is not the issue as well.
The RoonServer communicates to the client and the audio endpoints are built on the RoonServer PC. Anything that breaks/stops this communication will result in the endpoint on the client PC not being created.
This can also happen if one or the other PC has gotten the local network set to Public and not Private. Again, check both PCs.
Applications to check for exceptions in firewall. Roonserver, RAATserver (this one is important), RoonAppliance, Roon.