I found it. Again a quick downsampling to 320x200 of the animated GIF produced a valid SEQ with an import with the GUI version.
One thing that I noticed is that it is adding a black screen for the first screen. If you save multiple times it keeps adding one more. With the GUI I could just have it delete the first frame, but this would not be consistent and could remove a frame that should not be removed. I haven't looked through your class to see what may be causing it, yet.