One thing I noticed, at about 6:35 you go to sewing webbing. It occured to me that sometime, and I'm assuming when you started working with the SilNylon that you changed your Pressure Foot to one with rollers on it. I assume this gives less drag for the slippery, thin fabric. Then you've swapped to a standard style foot with rather large upturns on it. Assuming here to but the Lashing is not going to have problems bunching up, but it will be a little harder to turn and hit at a different direction, so the larger upturn?
And with the normal fabric of 3 or 4 vids back, just a standard foot with a medium upturn.
Maybe I missed or am imagining, it is late (3 am New Years Day). Happy New Year by the way. But if the foot change is desired, perhaps mentioning or an addendum somewhere along with pins, needles and cutting devices?
Basically, so far, you have covered most of what I know. There are pieces of the puzzle that you've solved for me. Tension, always a mystery. That Needle up, thread arm up thing. Who hasn't been bitten by that. And the bunch of stitches in one place, Pressure foot, bunch of garbage on the bottom, incorrect tension.
I've assumed seams all this time, but to have them put out and shown helped.