Have a look at the attached image. Why are there still visible seams with VrayTriplanarTex? Even setting Blend to 1.0 doesn’t fix the sharp seam.
I may be way off but.. it seem like image tiling (but blending normally)!
Yes, I’m aware of the image tiling. I intentionally used a non-tileable image to better show that the blending isn’t smoothing the seams.
Thanks for the suggestion and help so far, really appreciated. I did a test on a sphere and it turns out syncing these parameters is not the issue. I was under the impression that the triplanar map would also blur the texture tiling. However it blurs only the UV seams! In my first image there were no UV seams, just a texture that didn’t tile well so triplanar didn’t blur anything. So you still have to use well made tileable textures, triplanar will blur out only where there it detects seams in the UV map. So I guess this was a practical lesson for me on how triplanar works. 
Yes that’s the fact! I guess I wasn’t way off in my first answer (your image was blending normally)…
Unfortunately making tileable textures require a more sophisticated algorithm.
Hopefully will be implemented at some point! 
For now there is only UV seams blending (and it goes the same for, blend box map max 2017 and soulburns blend box).
Glad you solved it out and appreciate that you are sharing what you learned from this!