Hi earth-video,
Feels like the transparency is calculated wrongly. Meaning inverted, that would result in that seam typically. As usual, guessing is not my preferred way.
Please try this, and compare your PNG with the one attached in Photoshop.
https://projectfiles.maxon.net/Cineversity_Forum_Support/2026_PROJECTS_DRS/20260212_CV4_2026_drs_26_RSpg_01.zip
If you can share the PNG (Wetransfer, Google, Apple , Adobe or Dropbox only), if I can, I will have a look at it.
If nothing indicates, please check with tech support:
https://www.maxon.net/en/support-center
Cheers