i usually just use the smooth tool set to a very low strength and run it along the seams really quick. it levels them pretty well.
Hello
I see this is old problem, I found few answers but any solution.
I’m working with L3DT, but I see people have questions about World Machines too, posted many years ago.
I tried many solutions I found, use magic numbers like a scale * 1.001, * 0.1953125 rule of two, different HF sizes in pixels… all fails. Gaps are smaller, but never acceptable.
I’m sure somebody use world composition in Unreal Engine and can help me with this question?
For now my tiles looks like:
I have many sample landscape HF created, smaller and bigger, different tiles size, but problem I have always.
Please help++
Thank’s, this is always some solution, but I have large terrain with many, tiles and I afraid this is not possible in this case, and must be just correct import way. This is good for smaller terrain, but not very large world composition system I think. Not mention, smoothing can destroy coherent terrain created in other software - world machine or l3dt.
@ThompsonN13 Hello again. After some more research and tests I see it can be only solution. With exporting tiled HF always some problems, so smooth tool can work and be only real solution. I’ll wait, maybe someone have real plain import solution, but if you can change your comment to answer, I can accept it. Thank you! 
Here is the solution (had the same issue, solution is tested and confirmed):
The displacement is relative to the horizontal vertex spacing and due to the compression in the HFZ file format, which allows a small height encoding error (+/- 1% of the horizontal scaling).
Do this in L3DT:
go to the ‘File->Format preferences’ option in the L3DT menu,
select the ‘Project maps->Heightfield->HFF (L3DT)’ tree option,
Press the ‘options’ button, and set ‘DataSize’ to 4 and ‘FloatFlag’ to true (double-click to edit these values), then press OK to clear the options window,
press the ‘Make default’ and ‘Use format’ buttons, and ‘OK’ to clear the format preferences window,
re-generate the heightmap, and;
duplicate the tile borders (under ‘operations’, ‘heightfield’…).
Using the old HFF format in floating point mode means there is no possibility of compression-related quantisation errors.
Export the heightfield in tiles in the desired format again, reimport to UE4, and you should have a 100 % precise and gap-free result.