Unreal Engine 4.26.2, Landscape has black spots and flickering

Hello, I 'm new here. Sorry if this is not right place to post a thread.

I have high end PC, using Windows 10 with latest update.

Both 4.26.1 and 4.26.2 has the same problem for landscape. There are some inconsistent black spots on landscape in random areas and flickering. I noticed that first time, when I experiment with Sculpt of Landscape and creating painting materials. Could not fix it and didn’t find a useful information how to fix it.

I downloaded ContentExample from Epic, didn’t touch any settings and problem is still exists.

Here is my specs:

ryzen 5950x
radeon 6900xt
64GB Ram
1 TB samsung 970 evo

Also my wife 's computer has the similar specs but she have nvidia 2080ti and she has the same problem.

Here is a video:
(1) Unreal Engine 4.26.2, Landscape Black Spot Flickering - YouTube

and a sample gif
Untitled Project