I'm using Shadowflight breastplate and getting the rain of vengeance skill
I also imbued or transferred the one that grants knockback shot with frost and leaves trail in its path that chills and damages enemies.
The visual effects look the same as before and I don't see any trail
dealing damage to said enemies.

Maybe a bug - make sure that you did transfer it. And maybe try transfer it to something else and then back to the one that you want it to be