Several things to consider.
1: floating point precision.
Thats a distant piece of tile.
If the location of it is 100k from 0,0,0 and if you are observing it without any sort of world origin shifting - then the spacing peobably makes sense.
2: tessellation.
I don’t care who thought otherwise and added it back, its BS that should not exist.
If the issue is present because of #1 at 100km with tessellation multiplier of 2 the problem starts happening at 50km (pedestrial math as it may be very over-exagerated but it illustrates the point). - Vertex pun totally intended.
3: displacement.
When you use a shader to move stuff up and down, even with WPO on and only shifting the Z you run the risk of generating issues like these between supposedly connected meshes.
4: Hlods still being broken.
Its over a year, and im sure they are still broken/unusable.
5: world composition.
As everyone complains about it in the forum, if you are using it, then the issue is just that.
Revert to world Partition. Make proper landscape Impostors and you should be good to go (even with nanite).