I can actually see the text in the screenshot you sent in the popup however it is white on white so therefor not very visible.
This is very odd that it is related to a ProxyPass however is it possible a CSS is not loading properly? Do you see any errors in the network tab or the console tab?
Can you identify what aberrant CSS is added to make the text white? If so, I can try to identify why it’s being incorrectly applied.