Can you show us your setup? Is the text on the page itself or is it stored in an attribute? Or is it some other widget like a list? It sounds like it's most likely an issue with access rights or language settings.
I had such issue once, due to not setting the correct translation to my project language.
Did you check if the language is filled on correctly and that the project language contains the text you want to display?
Good luck with,
Assuming your pop-up is a Show message Action. If not, there could be other issues too.
1). Is the data visible in your log when you change the Show message Action to Log message?
2). Does the user has Entity Access to the Attributes in the Show message Action?
Go Make It