It's working, but munging the image

Yes, the plugin needs a rebuild using something more current like gifsicle. The only fix I found (although maybe useless for you if you have lots of users) is to use a service like https://ezgif.com/resize first then upload to media library.

Thank you!

BTW for what it’s worth, I read up quite a bit about resizing GIFs and apparently it’s very difficult to resize an animated GIF without dramatically exploding the filesize (apparently 4x-6x is not unusual).

I’m rethinking my strategy for how my site will use animated GIFs because of this.

More info: https://www.imagemagick.org/Usage/anim_mods/#resize