I checked the traffic through my network again and I found something further:
The Roon app is trying connecting 2 lan addresses all the time: 192.168.88.24:9200 and 192.168.50.108:9200. And all of these connections failed.
This is weird because neither of these is my lan address. My UDP lan address should be started with 192.168.17.x, and I confirmed that I’ve set the subnet mask to 255.255.255.0. Also, the ISP’s router’s lan address should be 192.168.71.x, so it’s not ISP’s router’s lan address neither.
Do you have any clue about these connections? Is there any service in Roon uses port 9200 as default?
Thank. you for your help!