Extra actions break, text colour

I am using the extra actions feature in the block editor to make breaks every 14 trials with a message in text to say this is a break. The background to my experiment is black. Sometimes when I run the blocks the break message text comes up in a white font and works perfectly. However sometimes when I run the blocks, the break displays a blank screen- which I can only assume is because the text message font is black for some reason. Is there any advice on why this is happening?

Can you please post the experiment that shows this behavior?