I really don't think it's an issue with the rig. I think it's something to do with the NLA, but I could be wrong. The only thing I noticed with your animation is if I add a new keyframe in the timeline with the IK controller, it will freeze in that spot. I think it's because you can't really mix regular timeline keyframes with NLA strips in that way. I haven't tried editing your NLA actions yet. I don't really do much with NLA strips, except if I want to share some actions with other people. I've been using the Animation Layers addon, which seems to do a better job layering actions.

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