I was working on a “framework” for an iOS app. When I added image resources, they did not work.
After Googling about for the answer, it seems that Apple added a setting for the MacOS framework template to combine related image files (like image.png and email@example.com) into one multi-image TIFF file. Since we based our product on that template, we had that setting. All the images were being put into files the iOS did not support.
If you have this problem, search your project for COMBINE_HIDPI_IMAGES. Be sure that it is set NO in all targets.