Any Ideas How to Fix Rotation Issue?

I have no idea why this is happening. I'm suspecting something to do with root bone? But not sure as I'm not an animator. Anyway, onto the problem:

I have an animator controller with two layers. Base layer drops straight into a blend tree that has three animations in it (Look up 90* with a threshold of -90, Look straight with a threshold of 0 and Look down 90* with a threshold of 90). The thresholds correspond directly with input Mouse Y and that works fine to blend between looking up and down in a stationary position.

On the second animator controller layer exists a walk loop that is activated by pressing a key. This layer is dedicated to player movement and uses a mask that simply disables upper body for that layer and only allows lower body to move for the purpose of walking; because I want to maintain the ability to look down or up while walking.

For some reason, when I press the key to start walking, the animation works fine.. but the entire player rotates on the x axis and the feet come off the ground. This only happens if I'm looking up or down. If I look straight it works fine and the feet stay on the ground.

Any ideas as to how I could fix this? I'm utilizing the RIFLE Starter: MoCap Animation Pack by MoCap Online from the Asset Store. Pictures of issue attached.