Day 39.
Looks like the N deficiency was the correct diagnosis. Unfortuantely I do not have any AN Sensi grow nutes, so I had no choice but to stop the AN Sensi Bloom and to use Biobizz Grow nutes I do have, until the AN Grow nutes arrive. Because of the deficiency, I've decided not to mess with half doses but to do a batch of water with the full dose Biobizz recommends. It helped - I've found no new yellowing leaves since. Next round I'll be sure to use AN Grow for the veg stage...
Her height is 36cm this morning, so she grew 9cm the past five days. I guess with having N deficiency, and my messing with the lights too much in the beginning, I'm paying the price in height. Still, I'm happy she continues growing and not stunned completely. I'm not sure how many more days are left before she stops vertical growth completely, but I'm hoping she has a few more days / a week left, that would put her roughly around 45cm or so at this pace, which isn't great but hopefully gives her enough space on the sites to grow some sweet buds.
For now, I'll continue to give her grow nutes + calmag until she stops completely. 300ml daily at the moment.
I think this photo below shows really well at what stage I've moved the lights up to the max height. Up until then, height is short and the leaves are fat, dense, wide. After the light's height increase the spacing tripled, and she shot upwards. I need to make sure that the next grow will happen under static lights at max height, because I bet if I'd had the lights up on max from the beginning, she'd be twice as tall now.