Image loading painfully slow in Universal Viewer, even with OpenZoom Layers enabled - how to fix?

Good afternoon,
I’m trying to load a file, which started out at 38 MB, and then I tried 9 MB, but they are both extremely slow to load in Universal Viewer. I tried enabling OpenZoom Layers hoping that the tile system would help, but it didn’t. Can anyone recommend what else I can do to make images load faster, at a reasonable time?

Note: I was just informed that there are some errors in the console that I do not fully understand: for instance:
“The IIIF server encountered an unexpected error that prevented it from fulfilling the request: the resulting file is empty or not found.
Warning : imagecreatetruecolor(): Invalid image dimensions”

and

Warning* : imagedestroy() expects parameter 1 to be resource, bool given in

Do these errors ring a bell for anyone?