I tried to crop/resize image, but the generated animation is broken or flickering. How can I fix it?

There are many different ways how gif images can be encoded and optimized, and sometimes ImageMagick (the program that does the actual resizing and other image processing behind the scenes in Ezgif by default) cannot understand them quite right. Here is one example, what happens when image cropping with imagemagick goes wrong:
Buggy GIF

ImageMagick is the best tool for GIF cropping and resizing due to speed, produced file size and good image quality in most of the cases, however sometimes it produces buggy results. If this happens, you can try to crop or resize source image again, but select a diferent crop or resize method from the dropdown menu:
GIF resizer method selection

"ImageMagick + coalesce" option will work on any undamaged image, as it removes all optimizations, but because it's slower and produces larger files, we didn't make it the default option. Gifsicle also can process most of the files, but the quality may be worse due to lack of anti-aliasing.
Fixed GIF