Variables text box disappears if variables change

Hello,

I put a text box containing two variables on the final screen of my OneNote eLearning. The two variables are recalculated when the timeline starts and should be shown in the purple rectangle on the second screen.

When the two variables remain zero (their initial state), the text shows up. When they change during the eLearning (which I simulate with the first screen in the file attached), the whole text disappears. Could you please help me with it?

Thank you a lot, 

Jan Složil