This is a very common issue and there all sort of recommendations all over the web to try and fix this. I've already mentioned the three ones that have worked for me in the past
But don't get your hopes to high, you might never get ALL your lan clients to "see" the server.
For you to know, "seeing" network shares in windows, is part of the netbios stack (nmbd), get wireshark and sniff packets in every windows computer to see if you''re receiving properly netbios broadcast packets.
You might have another lan client that you don't know that is acting as a server and becoming local master browser, who knows.....
I will re install this one that I am working on at the moment and if that doesn't work I will have to look for something else....
I am sorry but I run a business and haven't the time to waste on a product that doesn't work.
OMV is targeted as home user, you can look for another solution that fits your needs. But i wouldn't dismiss it because i can't see the server in the pretty network icon.