Hi Mark,
This might sound weird, and I apologize for asking, but have you enabled Alpha, or Straight Alpha, and are you using a format that supports it?
I have no problems here.
Example with all parts for one image with Ae file.
https://projectfiles.maxon.net/Cineversity_Forum_Support/2025_PROJECTS_DRS/20250818_CV4_2025_drs_25_PAcf_11.zip
I use straight Alpha here.
Cheers