If you were packing 20 pages, but now are getting 1000 with the same settings, then look at the images -- what is it packing? Check Debug
to see the packed images more easily.
What changed since you were packing 20 pages? If you didn't change settings, did you add more images or modify your images? Even then it's not clear why it would pack so differently. The most likely issue would be that you have unwanted images in the input folder that you are packing.
BTW, if you know your images will be a certain size, it helps to increase the minimum page size from 16. Otherwise the packer tries to pack each page at 16 and fails, then tries higher sizes until things fit. Since you have Power of two
and Square
checked, it'll go faster, but it'll still try 16x16, 32x32, 64x64, etc until it gets to a large enough size, which makes it take longer. Also checking Fast
will pack more quickly when you have many images.