Segmentation of polygons in equal lenght

Are you able to chop before it is buffered? Then you could try the custom transformer ‘DistanceChopper’
It works on polygons too, but then it splits the polygons to the outher lines and you have to ‘stitch’ it together again

I think I would use the Chopper to segment (a copy of) the linear infrastructure at every 1200 meter, then buffer the resulting segments. If you set the End Cap Style to None, the buffers will only be generated to either side of the linear feature, so should not overlap where they meet (depends a bit on the actual endpoints - if they are on a sharp change of direction, there still might be some overlap). 

The Chopper will chop at a determined length, but for polygon features that is much more difficult to calculate (hence the remark “approximate length” in the Help description). On a linear feature it should be more accurate. Or you can go the full LRS-mode, adding Measures then segmenting on the Measures - but that’s slightly more complicated.

You could try this:

Convert the buffer polygon to a centerline.
Chop at required distances
Insert a line on the cut point, rotate the line 90degrees (you can get the centerline azimuth)
cut the buffer polygon using the rotated lines