As for where your loop broke, YES, I've had that happen to me a couple of times before I figured out why.
When you Palomar your hook onto the loop it has a tendency to not hold tight especially with 40+ fluorocarbon. The line then has a chance to get into the tiny gap on the eye of the hook causing your line to be cut through while under strain.
To simply keep it from happening again switch to a live bait hook with a steel ring. Instead of fastening the eye of the hook onto your line you will be fastening the welded steel ring on therefor eliminating the line getting into the gap on the eye of the hook.
You won't have the problem again.
