Transparency Fails Intermittently When Rendering a Series of Long Semi-Transparent Tubes

I’m wondering if there are some secrets about working with semi-transparent objects that I still need to learn. I’m seeing an interesting artifact. I uploaded a video of the problem to Youtube (note: this is an unlisted link):

Each time that the tube becomes dark gray, this is the undesired behavior that I’d like to fix.
One tenuous explanation/theory is that when the center of each segment of the tube is out of the camera’s field of view, the remainder of the tube (that’s still visible in the scene) somehow loses its transparency capabilities.
I’m looking for any ideas for things that I can try to get the shot to render the transparent tubes consistently and with no artifacts at the seams.
Code that creates the tubes’ meshes can be found here: