Hi,
I had the same problem in the ue4 (4.22) editor and noticed that you must give the engine a little bit time to load the layer info.
You can also try to activate in the project settings the “Forward Shading” under Rendering/Forward Renderer. But this didn´t help me really.
I was also looking for a solution but after I waited 15 minutes it worked finally and the freeze was gone. It depends on your landscape material and the landscape size.
I hope I could help you 