Found that my second layer of insulation- Knauf R12 fiberglass was sagging a bit in my joist cavities. It's lighter and flimsier that the Roxul Safe and Sound I used in the first layer.
I can't let the insulation slowly come into contact with the drywall furring channel over time, so picked up some Simpson Strong Tie Insulation Supports, IS16-R100. Took a few seconds and did the trick.