The scanner used to plot unwanted pixels along the seams between terrain mesh patches all the time, but I have not thought much about them for a long time, so either the developers mostly got the upper hand on that problem, or I simply got so used to them my brain filters them out (I rarely zoom the scanner -- could be a bit of that, too). 
Presumably, other than through aliasing when sparsely sampling the mesh for the scanner display, and not accounting for edges, you would get a lot more of these sort of things if your machine is performing badly at terrain generation -- they manifest as the "kerb" you get between two adjacent patches that are of two different levels of detail, until generation catches up and matches them, so that they are the same resolution and incorporate the same levels of height-modifying features, and consequently line up with one another.
The patches do not reflect any sort of randomised tiles though, to my best reasoning -- the numbers that define the terrain are deterministically derived - otherwise the place would be different every time you get there; And while features do tile, the patches are not fixed prefab tiles -- they subdivide progressively the closer you get, and the layers of prefab bitmaps at various scales that combine to form the hightmap of the planets, are projected onto them, and across them, without needing to "slot" into them.
Presumably, other than through aliasing when sparsely sampling the mesh for the scanner display, and not accounting for edges, you would get a lot more of these sort of things if your machine is performing badly at terrain generation -- they manifest as the "kerb" you get between two adjacent patches that are of two different levels of detail, until generation catches up and matches them, so that they are the same resolution and incorporate the same levels of height-modifying features, and consequently line up with one another.
The patches do not reflect any sort of randomised tiles though, to my best reasoning -- the numbers that define the terrain are deterministically derived - otherwise the place would be different every time you get there; And while features do tile, the patches are not fixed prefab tiles -- they subdivide progressively the closer you get, and the layers of prefab bitmaps at various scales that combine to form the hightmap of the planets, are projected onto them, and across them, without needing to "slot" into them.
