Your interface is configured with a netmask of 255.255.255.0 or /24. This means that the first 24 bits (or three octets) form the network. In your case: xxx.xxx.54.0 is the network.
This means you can only see IPs from xxx.xxx.54.0 through xxx.xxx.54.255.
If you need to see IPs on the xxx.xxx.55.0 network as well, then you need to make your netmask smaller. You'll need to contact your network admin to find out what the correct subnet mask is.
(As a quick-n-dirty hack, you can make your subnet mask 255.255.0.0 or /16 and you'll see all the IPs from xxx.xxx.0.0 through xxx.xxx.255.255. But that's a bad hack, and you really should use the correct subnet mask.)
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