Rebooting (and ensure that Roon is fully updated) are “clear instructions from Roon.” If these don’t help then it’s most likely network related. Your network is not provided by Roon so they, and also us other users that try to help, can just give hints. The actual troubleshooting has to be done by affected users.
I move the thread to the support section of the forum (as users are instructed to do by the help article). Please make sure to follow-up with a filled-out support template:
### Roon Core Machine
<!-- Include your operating system and machine info (Model, CPU, RAM) -->
<!-- Write below this line -->
### Networking Gear & Setup Details
<!-- Your network gear (model of routers/switches), if on WiFi/Ethernet, and if you are using a VPN-->
<!-- Write below this line -->
### Connected Audio Devices
<!-- Specify what devices you're using and their connection types, like USB/HDMI/Chromecast, etc.) -->
<!-- Write below this line -->
### Number of Tracks in Library
<!--Tell us how large your music library is, eg. "30,000 tracks" -->
<!--Write below this line-->
### Description of Issue
<!--Tell us about the problem you're having in as much detail as possible. Screenshots are always appreciated! -->
<!--Write below this line-->
Further potential helpful reads: