Horn hook work well up a grade and uneven poorly laid track the problem is down grade with them and unrealistic appearance . When they get slack or crash together they release. Was this maybe per design
?
Jon
By the way the uncoupling pin is mounted, horn-hook couplers have a 'shelf', that keeps them from bypassing each other, built into them by default.
'Shelf' type knuckle couplers are available but, as Hunt mentioned, the most likely culprit is the vertical grade transition is too sharp. Which will cause couplers to lift out of each other.
Len