Just trying to help you out here, you can choose to do the above but it still doesn't solve your problem. Have you checked your build as follows?
1. After this step of installing just the lower arms, are they free? From my experience when building the kit, the 0.5mm spacers BB9 of the hinge pins caused binding as they were a bit too thick. I ended up using shims instead for reducing to 0.3-0.4mm.
2. Now moving onto the hubs, is the suspension moving freely after this step? There is a chance for hubs to bind here.
3. According to your description the problem may be somewhere in this step above. Before you assemble all the parts together here, lets break it down into smaller steps and checks.
3.1 With BC30 & BC16 assembled, is BC6 smooth if you pop them together?
3.2 Now pop the above assembly into the ball end on the arm (BB4 of step 14). Make sure you are using BB15 here as BB6 should not cause tightness if you follow the overall length of 27mm (ball links usually bind if the turnbuckle rod is screwed too far into the cup, which should not be the case here).
3.3 Now on the other hand, install only the rod BC28 itself (with 2x BC31) onto the gearbox. The rod shall first be centered over the gearbox by adjusting BC31, then adjust BC4 until it swings freely.
3.4 Now if everything checks out, connecting the turnbuckles to the rod by tightening BC30 should not cause any binding over the whole rear suspension assembly without shocks attached.
For step 19 in the manual, the indication of 1mm extension of the rod with BC30 should not be critical here, in general you want the BC6 turnbuckles to be at right angles (90degrees) with the roll bar when assembled.
Hope this helps