The Network folder is not actually populated by Opus, but via the Windows shell the same as in File Explorer.
Windows in general has never been that fast or reliable at enumerating network devices, and on top of this it also seems to have a separate cache for each process, so you may see things in one list which haven't been found in the other yet (and vice versa).
Antivirus and firewalls can also play a part, by blocking one program but not another from talking to things on the network, but that would usually mean you see nothing at all, not just a partial list.
Sometimes if you fully exiting Opus (via File / Exit Directory Opus) and then restart it, you may get a more complete list. (Or not. The OS is unreliable here, as I say.)
I think it may work better on networks with a proper domain/browser rather than the usual at-home ad-hoc setups, but I may be wrong. When I've been in the types of large corporate environments which have those things, the network was so slow (due to being international) and had so many thousands of machines that the Network folder had other issues. (That was before I was using Opus, and this aspect of Windows has not really changed much since.)
Something to test: Open Notepad.exe, use File > Open, and navigate that to the Network folder. Do you see similar results?