The light is or was possibly too close. Easier to assess that in vege based on node spacing. See some potential damage at the top. could be related to the droopiness seen, too. Pics are too far away to properly assess the leaf symptoms.
Canopy is a bit over-crowded, but nothing serious. Can also exacerbate what's causing the droop with lower transpiration rates.. plant can't "breathe" as well as it should..
Not much you can do about that. MAybe, remove a leaf or two, but removing leaves is something to avoid as much as possible. if some physical overlap is causing condensation on leaf surfaces, that'd be a good reason to remove one.
irrigation practices could be the cause of the droopiness, too, so the basics:
1) fully saturate (with 10% runoff minimum, if this is a soiless medium)
2) wait for appropriate dryback (or loss of weight) before repeating.
if not adhering to those basics, it could definitely be related to any and all problems seen in these pictures. You can get away with esoteric watering practices in the short-term, but over the long-haul it greatly increases risks of problems. "it worked for 3 weeks" is not an excuse to keep doing something wrong. Not all effects occur immediately after the cause.. sometimes there's a long delay or lag time before a problem is visible due to that behaviour..
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whether using lst or topping, should have a plan based on a target canopy, and get there the most efficient way without wasted growth and excess pruning etc... 2-3 colas per sq foot is all you need to maximize yield. With an autoflower, that's difficult becasue you don't really know exactly how long you have to train before vege growth ends. So, it's just a guess as far as how longn to train. I'd argue you trained a bit too long with this plant as there's very little depth to the canopy and vege growth looks about tapped out or nearly tapped out.
You want a bit more depth than what you have with a bit less over-crowding. i.e. Distribute / allow a bit more growth vertically. 16-20" deep is a good target.. realtive to growth patterns of various genetics...the lanky plants obviously can go a bit deeper and their structure allows more light penetration that allows for better nugs deeper into canopy. As long as either side of growth pattern spectrum isn't too extreme, doesn't make too much of a difference in outcome.
More colas does not increase yield. The light absorbed dictates potential to build plant mass. So, canopy size is more correlated with yield than number of colas. Training is just a matter of impacting distribution of that mass.