still image graphic's captions "jumping" after render

Hi, All -- Frustrating.  I created a video using mostly still images of my artworks (.tiff format), with a caption or title chosen from the available list of templates and placed over each still image.  The text "jumps" after rendering, no matter where I place it or how careful I am about not placing it within the effect wipe or dissolve area between clips.  Some captions are fine, and others jump or move for no reason.  I deleted all of the render files and started over with a new render, but the same thing happens.  I finally had to remove all of the titles because I was on a deadline.  What's up with this?  Frustrating, to say the least!  I'm working on the latest Adobe Premiere Pro 2020 update (14.9.0 - Build 52) on Mac Big Sur 11.4.   Thanks for your input!