Root motion translation in UE4 ignores Z movement unless the player is in for example a flying movement state. When in a movement state where gravity governs Z motion, the root motion translation ignores this.
It sounds like what’s happening is you DO have root motion, and Unreal is ignoring it. It might help to move your movement off of the root and onto another bone. e.g. Where you’re animating the armature object in Blender (to produce root motion), instead animate the highest bone IN the armature hierarchy (or bones if there are multiple direct children of the root, which is unlikely imo). Copy the locrot keys off of the armature object and paste them to the master bone, for instance.
Now Unreal won’t see the capsule attempting to move downward in the world, it will simply see the mesh attempting to move downward relative to the capsule. This should fix the issue, though it’s just a best guess without knowing more about your assets.