AJ,
I had just the same experience as you. I had been trying a bunch of different combinations for an Arbormaster DEDA lanyard. When I got something that was perfectly quick and reliable as a lanyard, it could lock up like you said.
My answer is “fat and soft” not “thin and hard”.
Tried several cords like 8mm UltraTech. Sewn and spliced. NG.
Then I went with plain old 3/8” tenex-tec, hand spliced, 27” i2i. The stuffed diameter is FAT as the Arbormaster and it’s very soft. The 27” length forces a really tight 4/1 Distle. It’s tough to wrap it and stuff it into the Pinto. But once tied, it is completely reliable as a lanyard, grabs instantly with no payout at all. But it’s so soft, it releases very nicely and reliably. There’s still friction as you take in lanyard slack. It’s as adjusting hitch, not a climbing hitch. But it’s an easy, smooth, reliable release.
Of cource, tenex has no heat rating but doesn’t matter for a lanyard.
OF