Repro steps:
1. Ensure you don't have anything that you can be profiled running
2. Open Profiler Window
3. For Active Profiler, select <Enter IP> and enter "127.0.0.1" *
4. For Active Profiler, select 127.0.0.1 from the list
5. Your editor should now hang (if it doesn't, try selecting 127.0.0.1 again)

Ensure you have no player running that can be profiled on 127.0.0.1 if you can't repro.

* (Step 3) This spits out the message:
Attempting to connect to player ip: 127.0.0.1 with a 1 ms timeout
UnityEditorInternal.ProfilerDriver:DirectIPConnect(String)
UnityEditor.AttachProfilerUI:SelectProfilerClick(Object, String[], Int32)