I doubt that is a problem but maybe. Hard to say without seeing it. The DF vines bend over the top of the supports and get loaded with weight and dont seem to slow down at all from bent joints. As long as the central vein is intact they seem to be fine.
Is the S8 plant sharing root space with other plants? Was it planted after the others? One thing I noticed is you can't put a new cutting into same rootzone as larger plants. The roots DF are like a big sponge and quickly crowd out their container or planting area. Once theres mature plants on a support you cant add a new cutting.
Here some pics so you can see clearly what I'm talking about, the situation doesn't look right to me already, but with such a twist I'm afraid that as both stems grow thicker they could strangle (more) the cambium:
At the top the Sugar Dragon measures ~2 meters (~6,5 feet) with not branching still, it was planted in June 2018, the same day that Cosmic Charlie and Halley's Comet,in the same spot, with the same soil, same fertilizing and watering program, S8 is 2 meters and not branching yet while CC and HC grew like pitayas normally do, with a lot of new branches and both gave flowers this year, actually HC is right now with 4 fruits.
Here the top of S8 and in my hand a Connie Mayer I planted on May 26, 6 months ago, is almost as high as the S8 and still growing.
CC and HC are also both growing right now:
So something must be wrong with the S8 when is growing so much slower than the rest under the same conditions. I'm thinking of cutting in spring by that sagging joint, let the plant start over a new, straight stem taking profit of the original root system that is already in the ground, and move the old long stem to root in another spot, with a good mix, since anyway I was planning to propagate this variety. All this I'd do in spring.