Issues with choiceBoxes in javafx when it isnt on the first screen, how can I implement choice boxes when it is on different screens?

I have an issue with the ChoiceBoxes in javafx, where I cannot implement labels in the dropdowns of the choiceboxes. This is not my primary stage, and it works when I set this to the main stage. I implemented the initialize() method for the choicebox, but whenever I try to run it, and it isn't the start stage, it doesn't work.

Does anyone have any idea how to fix this? Please ask if you need any further information, and I will be happy to comply.