Some JPEG files load correctly on the SLCD5+E, but files of the same image in a Progressive format, do not load.

The Progressive format of JPEG files can use a large amount of RAM, which, with large images, can easily exceed the RAM available in the display module. The fix is to not use the Progressive format and to stick with the Baseline format. More details can be found here: https://kb.tourwriter.com/baseline-jpeg-vs-progressive-jpeg