I think @Indacut is probably on the right track. The flower stretch combined with lower DLI in flower will make some pretty leggy plants. Even more so with most sativa dominant strains.
As for the weak stems, I’d guess it’s a product of high N levels. The fertilizer stakes have time release N that could lead to excess in mid flower when the demand for N drops. I’m just not sure how long it would take the constant runoff in coco to flush it all out. It may not even be there anymore.
The strengthening aspect of airflow comes from moving and bending the stems just a little. the same thing is achieved by just handing your plants regularly. Training, pruning, and inspecting your plants force you to give that same stimulation with your hands instead of moving air. Anything more than a gentle breeze fluttering the canopy for an extended period of time can create too much damage and the stress will outweigh the benefit. We want tiny amounts of damage so the plant can easily recover stronger. Too much and they will be damaged faster than they can recover, thus the strengthening doesn’t happen, just the opposite in fact.
Ihy. Yeah, even if just my head brushes against them when I have to get in between them to water they break. It’s a circus act trying to get in there. Tonight I started just removing the outer ones from the tent long enough to water and get my test samples. What a pain, huh??? Such is Karen’s World.
This weeks photos. There’s some crisping at the tips of the leaves, but idt it’s something to be concerned with right away. We shall wait and see. I am including the 2 Autos I have going. I’ll tell you what, I have zero luck with them. The Lime Glow have been 8 of 10 so far with terrible results. The Apple Fritter seems to be doing ok except for being as small as it is, about to start week 8. At least I will get some personal out of it. Pretty sure that other than the 19 seeds I have left of it, I am done with Autos. Might not even plant those.
Idky they never post in the order I upload them. I even did 2 and 3 at a time this go round and they are still out of whack. 
You can arrange the pics by cut and copying the strings int o the order you want although I haven’t had problems with them getting mixed.