Stained Paper and debris in vents after duct cleaning

Hi Pros,

I had duct cleaning done yesterday (roughly a week after a furnace replacement + new AC was installation). Few minutes after duct cleaning was done, hovering under and around the floor vents, I noticed sponges like dark material from m&m to golf ball sizes. An hour or so later, one of the floor vents had a white wafer like paper either stained or burnt brown on the edges (roughly size of a business card) under one of the vents. Found a smaller similarly sized piece the near another vent this morning.

Never, seen these before Yesterday. Should I be concerned about damage to the ducts and can these things be harmful?

Any response is much appreciated.

Thanks,
stead123

source https://hvac-talk.com/vbb/threads/2227468-Stained-Paper-and-debris-in-vents-after-duct-cleaning?goto=newpost