The problem is that value:
View attachment 94983
This parameter is the distance over which is mapped the specified terrain. For example if you put 1000.0, the game will reproduce the "Laythe" terrain over 1000 meters, then it will do the same for the following next 1000 meters, and so on until the circumference is fully mapped.
It's suitable to have a terrain mapped an integer number of times, so that the mapping algorithm doesn't finish the job while still not having reached the end of the terrain.
In your case the planet radius is 129000 meters:
View attachment 94984
So the circumference is:
2×π×radius = 810530.9m
Your terrain is mapped over 3141592.6 meters, it cannot even be mapped once entirely because the planet circumference is not that big. This results in that anomaly because the last point doesn't have the same altitude as the first point.
You have to use 810530.9, or that value divided by an integer, this should solve your problem.