Hello Iby,
If you are using Displacement or World Position Offset in your landscape’s material, then the flickering you are seeing is more than likely a bounds scale issue. What that means is you are pushing the vertices of your landscape outside of it’s default bounds, which defines whether or not that particular landscape component is culled or rendered.
There is a visualizer within the viewport you can use to see the bounds of any object you have selected. Below I have outlined a quick example of visualizing your landscape’s bounds, and modifying the ZExtension in the positive or negative direction.
Bounds Visualizer
Here you can see the bounds of each landscape component.
Default Landscape ZExtension
As you can see when using Displacement my landscape also flickers and renders with missing components.
Modified Landscape ZExtension
Once I modified the ZExtension values, the flickering goes away. Be sure not to extend the bounds by too much as it can begin to cause performance issues.
Hopefully this helped and let me know if you have further questions or need additional assistance.
Cheers,