I ran into a weird bug where my 3-bone IK chain isn't behaving as expected. I've made other quadrupeds in the past and had no problem like this. As far as I can tell, the IK constraint is also exactly the same as all others I've made. Here are some GIF examples.
This is what I would expect from a good 3-bone IK leg: https://gyazo.com/98754f4cdb2f08d87d9ce5734c5b367e
This is what I'm getting now, the upper bones are barely rotating: https://gyazo.com/0ea27bb19a79a998cf1cfe44400b36c5