I am using 8.91 and having the issue of jpg images not showing in the exported video. I have several jpg pics, which have been used more than once across multiple tracks. Their original duration was 3s, but in the various tracks they have been extended, and all appear correctly in the sequence preview for the correct lengths. But in the exported videos they don't appear at all.
As a side note, in the preview the images all have grey borders appearing around them, even though there is no such border in the original pic.
*EDIT - I created an empty file with just a jpg on top of a blank (separate tracks) and it exported fine, so there must be something different about my original project file.