In my experience ( and believe me I've cooked a few seedlings in my day) if it was heat, the whole seedling would be shriveled up. Your shriveled up growth starts right at or above the soil level, which is classic damping off. Picture attached I think shows it pretty clearly.
Went back and...
That was definitely caused by damping off. That's pretty much a textbook picture example of what it looks like. FWIW, I always spray mist the top layer of soil in the pots with this, and I haven't had a seedling damp off in forever it seems like.
OR option B: If you're not in a hurry, you could get at least 2 clones the same size as the bottom third from what you cut, get them rooted, drop them in a pot and give them a couple of weeks for the roots to develop good, and then flower them out. Big tent for just the 1 plant. Set you back to...
You could cut that down to about 1/3 of it's current size, put a screen up and supercrop it. Make a bunch of clones from what you cut and have mature plants ready to go for your next run. But if you just want to remove some growth and flower it out, by all means, you can def do that.
Does appear to be missing growth at the top there, which is ok as the side growth at the top node is taking off and will now be your top. It's not a big deal. Looks like whoever made the clones probably had enough on that cut to get more than 1 clone from and did so
Also, just my opinion (worthless in all 50 U.S. States and satellites, and all foreign potentates *may have some weight in Gelderland*) on the stipule theory: I've seen that floated since the early days on the original Overgrow (late 90's) and I put zero stock in it. But I'm willing to be wrong...
Pretty sure I can see the white pistils sticking out of the top of the preflowers on E, so yes, female, pending a better look.
Based on the shape of the preflowers on G, I'm going with female also, again, pending a better look at them.
You know you can buy ya a 30x loupe off that site that sells stuff that everybody orders from for like $6. Preflowers will show up right there at the nodes by the stipules. Lot easier than taking pics that we may or not be able to determine what's up from.
What does the growth above the split look like? As long as it's strong and green and reaching for the light, I'd not worry about it much. As far as the split goes, I'd wrap a pipe cleaner around it and snug it up and forget about it. You can get a bunch of them at craft stores for pretty cheap...