Day 19 pre-flower and stunted growth?

if it didn't stop, it's probably just more spread out... when you break apical dominance, which is what LST does, you shift allocation of resources in the plant. and i'm just making these numbers up for effect -- you may have seen 1" per day when he plant was focusing on 1 dominant, highest growth node on plant, but after it gets shifted to multiple growth nodes it gets spread out... may still be more in total or not? that is uncertain. what is certain, is that you can more effectively fill a space with an even canopy this way.. break apical dominance of any limb that gets taller than others until they catch up, then releas it... continue to do any longer-term LST as needed. manipulating apical dominance to shape the plant's growth is a tool. mix in some topping where appropriate. Just depends on the context. if i need 2 colas in that area and it's a bit ahead of the rest, topping is an excellent option. it slows it down a tad while the 2 new growth tips start ramping up growth. 2 birds, 1 stone. timing must be right for that of course... don't be afriad to remove some growth,either. LST typically results in more vertically growing branches than necessary. train it out wide or prune it off... "Low stress" is in the name, but that doesn't mean it doesn't stress the plant. LST can even cause some odd leaf growth -- non-serated leaves, atypical number of fingers etc... it may even cause an auto to flower. it could be a culmination of things and it was merely the straw.. all depends.. messing with autos is a bit of a risk in this regard... i don't think it's very common but you'll see it if you always train/top them at some point. you should have good vege growth (stem elongation and new leaves) through day 30-40ish or even longer with "XXL" autos.