If the second field ( right pane ) in the value list selection is text and you actually have the second field formatted as number in your field definitions then it will display ? when you pop the field if the value is text only ( no numbers ). If it contains any number then FM will index it, ie, 123abc will work, but without a number in it, it will produce ?. You can verify what will work by entering the field (either while edit box or drop-down) and typing CTRL-I to see the index. Is this what you are experiencing? This issue would also be present with drop-downs however so it may not be your issue.
If the second field is NOT number by accident then it might be tied to an existing bug with version 12.0v3 on windows with pop-ups where they do not properly display until the format is changed from general to as entered in Inspector > Data > Data Formatting.