Hi, fellow user here. I do not know if this is going to work.
Power down all. Router, computers, endpoints.
Wait some minutes.
Power your router, than switches, than Roon Core, than all the rest one by one.
Maybe if it doesn’t work get in your router settings and review all ip’s and settings.
Other users might help you better than me if you use the template for support (provide detailed description of your network and setup, etc)