Do you use any Norton (Symantec) security products?
I use Norton 360, and recently upgraded it to their Windows 10 version of the product. It is an entirely new interface, and it seems to have had some of its intrusion protection functionality significantly beefed up.
This gave me quite a few problems for days, as it was blocking communications between the server, client, and JRiver servers, on some but not all functions. I possibly could have just set MC to be allowed to do anything by putting an exception rule in, but I prefer to use their automated detection methods and then allow the process to complete when a popup asks if it is okay. So popups must be turned on to see what is going on. i.e. Silent Mode must not be turned on. I think it took a few restarts and some use of MC to get all issues resolved, partly because I upgrade the client and the server/HTPC at different times, separated by days. Symantec don't force this significant upgrade on a user immediately.
I believe that other Symantec products have recently gone through a similar upgrade.
Of course, other security products may be going through a similar process to ensure compatibility with Windows 10, particularly if you have automatic upgrades turned on. I'm still on Windows 7, but still had these problems.