Bug with animation slots?

Problem: animation montage plays only on the lower body despite being assigned to the default slot.

I’m using layered animations.

I have Default slot and Upper body slot.

I Created a montage and assigned it to default slot since I want it to play on the entire skeleton but it only plays on the lower body.

This is a new problem. I have another, older, montage built on the same blueprint and skeleton that uses the default slot and is successfully played on the entire body.

For testing I created a new montage and put two animations into it.
The first animation isn’t working properly. Only the legs animate, the second animation performs as desired with the whole body crawling. The montage is assigned to default slot.

See the video. Notice how only the legs are animated in the first half. Don’t mind the crazy rotation that happens at the end of the montage, thats just part of the animation.