Now that you've gone through the TFSR pages, I'd like to see the results of the link from my page.
http://www.archaicarcane.com/fragile...-equal-stress/
I suspect that the tension is still a bit too tight, and it just reaches a point where it snaps.
The bobbin thread being pulled up despite the loops on the bottom is strange. I suspect that it may be getting caught around the hook area. There are a few things I can think of that would cause that, and some are tension related.
Can you post a pic of the hook area with the bobbin case in place and with it removed? With the case removed, I'd love to see a clear photo of the tip of the hook, the part that would grab the needle thread. That will let me rule out a bent hook tip. (very unlikely)
What does it look like when you turn the hand wheel with the needle threaded? You should see the needle go down, the hook (you won't really see it with the bobbin case in place - but leave it in place or it won't behave correctly) will grab the needle thread, and pull it a little more than half way around the bobbin case, then let it go. At this point, the take up lever will pull the excess needle thread up, which will form the "knot".
Is this what it looks like when you turn the hand wheel manually and watch the hook / bobbin area? Or does it seem to get caught somewhere?
It's rare to have a problem with the hook itself. Usually it's something "silly". Even if it's timing, I can walk you through that. Physical damage to the hook is the only thing we want to avoid. I've straightened a bent hook. That was nerve wracking.