Issue adding network in advanced way

I have several Networks in my system. And was adding one more, want to use certain Ip range to that network and tried to add that via advanced “mode” I did add start Ip and end Ip and submit. Network comes visible. Auto-assign is on, but memebers does not get IP’s.
Adding Ip range in easy “mode” and right away memebers get IP’s.
I’d like to follow certain Ip scheme in my networks, so what I should do to use advanced “mode” adding Ip’s under networks