Regression: Tested in UE5/Release-5.0 at CL 20979098, this issue does occur so it is not a regression.
This issue occurs if the scale set for the landscape has a decimal value that is not 0.5. Setting the scale to 0.5 (i.e 10.5, 50.5, 100.5) does not show a seam. Values between 0.1 to 0.4 and 0.6 to 0.9 do show a seam.
Actual Result: Seam is visible in the landscape that splits it into 4 quadrants
Expected Result: No seam should be visible after creating the landscape
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-174155 in the post.