P.S.......Sure youre probably already aware of how to LST a plant, but in the future (incase you dont know this alternative technique to LSTing) Here's what is personally done when LSTing is to soften the stem first so it is more pliable and not so brittle.... (and not just bending it back and forth slowly, this is a much different technique
Take the stem/branch (whatever you want to train) and first spray warm water on it with a diluted solution of vitamin b(superthrive or cloning gel/powder) it will be absorbed into the stem to help the plant heal the cells inside as anytime you are bending a branch you are collapsing thousands upon thousands of plant cells inside and also compressing the vascularity/veins in which (chlorophyll other proteins etc...) are traveling through. Normally when LSTing these cells generally repair rather quickly and just slightly delay the growth of the branch, but in some cases it damages beyond adequate repair like in your case had occurred.
When LSTing do this next time.... again spray the point of where youre going to bend the stem/branch (not the whole stem LOL
with warm water(drop or two of vitamin b suppliment mixed in 20 oz or whatever spray bottle or larger) about 20-30 times until the stem where your going to train is soaked well. Why warm water? Because, the warmth of the water will make the cells in the stem/branch swell and it will stretch the cell walls so its like stretching before you go running so when you go out there and do a sprint you dont snap a hamstring and lets just say HOLY FUCKING SHIT THAT HURTS LOL
haha anyways your going to make sure that the water is not hotter than 100 deg and 90 at the coldest.) After your spraying the first time dont bend the plant just yet give it a couple of minutes to swell then let give it another 2 mins to cool off. Repeat this process 3-4 times until when you gently push on the stem/branch the point of bending should be much softer(some strains have different thickness/hardness to their stems/branches so its all relative to your specific plant. Here's the trick, instead of bending it, try a gentle twist and roll over (again this is like a stretch for the plant and not snapping
(this way the stem/branch will still maintain all of its structural integrity and substantially less damage will occur to it.
As always.... enjoy your grow