Thumb height initially set to 0px

[JMantis0]

Confirmed the thumb height is starting out at 0px, and only becomes greater than 0px if the mouse wheel is used to scroll within the concerned element. I've also noticed certain state updates within my application will cause the thumb height to increase above 0px.

I am expecting the thumbs to appear and have the correct height when the component renders, similarly to the demos.

I am not sure what I'm doing differently than the demos.