AME vs PP Keying Issues in Renders

Working in the latest PP and AME on MacOS Monterey, I am encountering a strange issue where keyed shots (using Ultra Key) render in AME with the background getting shifted and/or scaled. It appears to be caused by applying Gaussian Blur to add bokeh/separation to the background. (I see this rendering to both Quicktime and h.264 (mp4) in AME. Yet the problem doesn't exist when rendering directly from PP. Thoughts? Ideas?
TIA.