My HH support line used to slip every night, before I started using hardware. I have been using figure nines, now switching to rings. No slippage during the night... until earlier this week.
Turned out it was the tree huggers! Each one slipped just a tiny bit, a couple of times during the night. You could just make out the slippage marks on the bark. It was a cold, dry night. The trees were not smooth barked, but rather tough and hard. Sorta puzzling that the huggers would slip at all. Anybody ever have this happen?
I lost one of my original Hennessey tree huggers. Now I use a pair of one inch Eno huggers with multiple loops spaced out along one end. Using the loops, they are never cinched tight to the tree.