Scoundrel’s Leathers never spawns Caltrops for me. It might be because I’m using melee core skill (TB) and Caltrops require distant weapon (edit: they don’t require distant).
Edit:
I think I found the problem, because I managed to spawn Caltrops after trying different methods.
It started spawning Caltrops after I equipped it on skill bar.
When you equip Caltrops they start on cooldown and they also sit on cooldown “in background” untill you equip them and let them go off cooldown. After the cooldown ends you can swap them in and out of skill bar and they will be off cooldown.
By doing this I was able to swap them out of bar and still spawn Caltrops.
Sadly after I teleported to city they went on cooldown again “in the background” and I need to repeat this process.