Q: i see double wifi ssid on wifi network list

It seems that osx cannot see roaming access point ssid like did before. We have 4 access point with the same ssid. On other osx works flawlessly, infact they see an unique ssid for all access points in the wifi network list. How can i resolve that?

I tried to delete this ssid network from the network advanced preferences and create again but nothing has changed. It's strange that in advanced network preferences i can see only one network with this ssid and not two.

Please can you help me quickly because it's my boss mac and i can't imagine how resolve it.