I have had a lot of trouble with this as well. I tried switching to the GD library but that didn’t work.
What does work is to keep scaling down the image dimensions until it succeeds. It’s not the file size or permissions. It’s the height times width dimensions.
For instance, a height in pixels of 2400 for a particular image will never work. But a height of 2350 will always work. An image of greater width would require less height to succeed.
When it fails, the image has uploaded but failed to “crunch”. That is, none of the smaller versions were created. Could be a limitation of the working buffer size in the graphics library. Maybe somewhere around 3.5M pixels.
