If you are using DHCP on the router (all do by default), it assigns addresses automatically and they may change.
Some routers allow you to enable a setting so that DHCP still assigns the addresses (which is generally preferable because it ensures that the same address is never used for more than one device) but it’s always the same one.
Decent routers have a name server (DNS) for the local network, so that you can use names instead of plain addresses. Then you can use the device name in Roon and everywhere else, and the address does not matter. These names should be listed in the router’s admin web page, and you can also change them
I don’t know the Nighthawk but seem to remember that it’s a good one. Check the manual
I got my library back… I did a error check/repair on the hard drive. Then used the ‘Eject storage device’ icon and plugged it back in. I hope I don’t have anymore problems. @BlackJack , Thank you for the advice.