Vertical Velocity Reset From Call to Set Flipbook

I have a simple movement animation state machine set up, yet when incorporating it with my movement system, it resets the player’s vertical velocity. Basically, when I jump, if I press another key, I slow my fall.
The following are the scripts that manage it. Where is the error?

I have narrowed it to the ‘set flipbook’ method call specifically, yet that doesn’t explain why…

I am still uncertain as to how I should proceed.

As much as I hate to bump posts, this problem is really stumping me.