This is the situation.. Anyone know the possible source of the problem?

Thanks a lot in advance!

That looks like the border of two 'cells' to me - though I could be way off mark!

I had the same or a very similar issue when building an island from scratch (new world space).

What I did was simply 'Soften Vertices' to effectively join the two cells. This was done in cells that are under water and not important to the mod though and I can see from your linked image that this may not be a viable fix for you.

At the moment, that is all I got to try to help - sorry I cannot think of anything else.

Tkx anyway UKNightWatch If anyone else knows a workaround to fix that thing, please, help XD

As UKKnight said a soften between the cells woudl fix the issue ....

if is a custom created land shoudl be fine , if is instead an editing of a vanilla terrain it may be problematic to alter the position of the terrain layout in this case I suggest you to redo your steps befoure the problem arose...

I did a new worldspace without any parents truth be told! Dunno the pics I posted just show the minimum problem I've been having with the current issue :\ The fact is that if its "small floated terrain" the soften fix works well, already tried that one before in other worldspaces, but when it comes to like a 50 points height of distance between land, well. SUX XD

well try to lower the terrain for that cell in cell editing windows then ... not sure if is possible tough never tried or try to fix the heightmap used ...

Here another screenshot that explains better in view!