Oh god. Could this be a bug from 4.6? Inconsistency of animations on Build/Standalone Mode - #2 by anonymous_user_280dd372
The video linked is private (or at least it does not load when I click it), so I can’t verify.
But I really hope not.
Another possibility, newer: AnimBP: Layered blend per bone Doesn't work in Standalone / Packaged UE5 - #8 by OneHundredFeet