Regression: Tested in UE5/Release-5.0, issue does not occur so regression is yes
This issue appears on whichever side of the first landscape the second landscape is adjacent to. Moving the Directional Light in the scene changes the shadow's angle as well, but the behavior should match that of 5.0.
Actual Result: A shadow appears on the first landscape near where the two landscapes meet as if the first landscape is going under the second landscape.
Expected Result: Both landscapes should be lit the same and not have a shadow on one landscape where they are close.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-173355 in the post.