Since 4.26 the landscape editor eventually tends to crash UE. Now with 4.26.2 this appears to have been become even worse.
With a newly created standard landscape, with or without material assigned the editor will crash after a few edits with the landscape editing tools such as sculpt, erosion, or flatten.
Perhaps someone found a trick to edit the landscape or can point to a hotfix commit? So far I am able to make 1 or 2 small edits, save the map then the editor crashes.
It appears that this is happening if you use an existing Landscape Layer Info file, even when that file was previously used for the same layer, and is no longer in use (deleted Map).
Thus, the solution to this problem seems to be to setup new Layerinfo files.
Update:
Even though I could work longer after assigning new Layerinfo, after a whiel it crashed again 
Partial Fix
In 4.27.2, the only way to edit (overly complicated) landscape without crashing is to right click the layer in the sculpt window, export to file. You get a black and white image in the form of a png file.
Opening this file in a graphics editor, you’ll notice that you get various shades of gray, and if you can recognize your landscape, you’ll notice this is your height map.
I use GIMP to edit mine, but you can use photoshop, paint.net, or any photo editor that handles png files.
When you are done editing your height map, right click your height map in the sculpt window of the editor, and click ‘import from file.’ It works surprisingly quickly.