So I ran into an image rotation issue with _display.jpg files. I use CaptureOne as my external editor, I edit a raw image and process it to a _display.jpg in the same folder. Mylio sees that _display file and uses it for the thumbnail/preview. That’s all good.
The problem was with a second computer that is NOT a vault. When my _display.jpg files sync’d over to that second computer, the images with the _display.jpg suddenly rotate 90 degrees.
If, however, that second computer downloads the originals for the problem images, the issue resolves itself. So it appears that the _display.jpg is having trouble on non-vault devices.