Video transparent when image placed underneath. Object Masking lasso used

Thanks for the report.

Just so I understand correctly:

• You used Object Masking to isolate a subject from a green screen clip.
• The masked subject appears correctly when placed over video clips, color mattes, and black backgrounds.
• However, when the same masked clip is placed over a still image (JPG, PNG, etc.), the subject becomes partially transparent.
• The issue also occurs with clips that have not been extended using Generative Extend.

A few questions:

• Which version of Premiere Pro are you using?
• What type of image files are you using as backgrounds (JPG, PNG, PSD, TIFF, etc.)?
• Does the transparency occur with all image formats or only specific ones?
• If you nest the masked clip and place the nested sequence over the image, does the behavior change?
  
  Here to help
  Ian

Very odd: have no idea what is going on here.

Please post screenshots of Program monitor, timeline and Effect controls with relevant properties showing