While [P]illager beasts already have a small shadow in comparison to the similarly-sized iron golem (MC-138766), they also have another issue with their shadows; specifically, it starts at it's front legs, rather than being centered at the center of the mobs body. So even if the aforementioned shadow size issue is fixed, it would still look very strange the way the shadow is placed now.

This issue was also present in the Minecon Earth 2018 footage; one scene shows a side view of the beast.

I believe this bug might have started occurring after the changes to the lighting system were implemented.

Edit: Oof, I'm dumb. This might actually be the exact same thing as MC-138766.