I have extactly the same problem, I have Roon server installed on windows 10 and Avast installed. In the last few days the core was “invisible” for clients. If I disable all Avast protection the core become visible again. After connections I can enable again avast protections and Roon still works. I tried adding exceptions without any luck. I tried to selectively disable single protections since I found that the problem is ransomware protection. Adding Roon server to Ransomware exceptions doesn’t help but only disabling of the ransomware protections. The problem is that I don’t like to have that protection disabled and it’s boring enabling that after connection or maybe I could forget about doing it. It’s strange though that ransomware protection of two different antvirus software (avast and AVG) lead to the same problem