I didn't think senescence was an issue with cannabis clones. Which makes me wonder if some wandering, traveling, soil gnat transferred a disease (fungal, mold, lower fungi, bacterial, etc.) into your soil. After all, if it's not genetics - it's the microbes and the way they digest the soil.
Check your soil bin for strange smells - other than those with which you are familiar (we - like dogs - have a pretty acute sense of smell). If it's musty, you have a cobweb mold over-abundance............etc.
**Topic Followed**
Yes this is exactly what is suspected..

Fasciation can be caused by several possible causes...
Such as Genitics (Which I can quite confidently rule out as I've been growing this particular strain for a very long time and has always been consistent).
Environmental causes - My grow is quite consistent and the only time there are changes are from winter to sumner with slight temp incresses.. but this occured during winter with no noticeable changes so I'm confident this wasn't the cause.
Hormonal- This could factor into the cause as I have experimented with BAP (6-Benzylaminopurine) on a select few of my Cacti. While I was quite careful with the use and and applications I can't be 100% positive. But tools I used were specific to cacti and conducted in the kitchen well away from my grow. And always cleaned up and disposed of pins after use. Cacti were grown in a separate room, which is it my flowering room and this plant was already flowering when the BAP arrived and I started experimenting with it.
A more likely cause is either Bacterial, Fungal or Viral. While I didn't see any noticeable pests that that could have transferred anything; it is quite possible as my grow gets pretty busy in the winter.
Some things to note: the stem if the plant was squashed flat.. so Unlike a normal Cannabis plant with round stems this stem was a good 1 inch wide by 1-2 millimeters thick. Shitty I can't seem to find a proper picture of the stem of this plant.. but you can vaguely see what Im talking about i the pic's below in the lower portion.



Growth was heavy on the growing tip and very light below the actual flower head.
Was an interesting plant to watch develop. The cola even forumed an S for Skunk if you look close enough. Hasn't happened again and I've run these clones multiple times since.

Skunk