Hey! Thanks for the reply! Unfortunately I can't really share the file but I'll try and explain it better.
So I imported the old file with working IK animations and had both skeletons in the same file with mostly the same bones and animations. I can drag the animation state and bones/images from one file to the other and every thing transfers and works, but you can't bring over the IK constraints, only the targets for controling the IK transfer over.
So for instance I can drag the red IK targets on the left to the new file but the IK connection icon on the right doesn't transfer with it:

I guess I'm mostly just wondering if there is a way to transfer the IK constraints from one file to the other (either through importing a skeleton or another way) if all the bones and everything are the same. You can't seem to drag them and they don't come over when you drag bones with IK connections on them:

Hopefully that makes more sense