Visibility Issue with CustomBrush_Landmass in Unreal Engine Landscapes

I’ve been having an issue for a few days with creating my world. I’m using CustomBrush_Landmass in the landscapes. The problem is that when I increase the size of my landscape, the custom brush becomes invisible, as if I had pressed the little eye to hide visibility, but that’s not the case. So I’ve tried everything to bring back the visibility of my custom brush. For that, I’ve reverted back (ctrl Z). Additionally, sometimes when creating another landscape, I can’t get the 3D view of the CustomBrush_Landmass, and I don’t know why. It should be visible, but it’s not. Do you have any solutions?
My goal is to create an open world, and currently I’m stuck because the CustomBrush_Landmass becomes invisible when I increase my landscape with add in manage.
By the way, is increasing the size of the landscape the solution for building my world, or should I have many different landscapes and then merge them together? Is it possible to merge them together?
I hope you can help me, have a good day!