Fear not, I got ya:
Essentially, the component holds onto a widget - it maintains its lifespan automagically; it will create it and destroy it as needed.
We need to dig into the component to get that 2d widget. You can then right click the pin on the cast node (green arrow) and Promote to Variable.
From now on, you can access the widget directly. Use this reference to get the vertical box.
What I think was happening - the component had a widget already but you were creating an additional 2d widget and manipulated that new widget’s vertical box, not the one the component had.
A bit of a guessing game but that’s my best bet at this point. Do tell how it goes!