Try making the field wider on the layout. If the field is too narrow to display the full, formatted value, you'll get a question mark.
But your calculated results here are of mixed type, mixing number and text results in the same field. The "No 1st Response Yet" results may also be affecting your results.
You might also rewrite your calculation to make it simpler:
Case ( first_response_date>0; first_response_date - report_date;
zcClosedText = "Closed";close_date - report_date;
"No 1st Response Yet")
Well as they say you nailed the reason for the "?". I made the fields wider and no more "?".
I am trying to think of a way to not have to put the text in those fields without throwing the summary off (aka just leaving the detail field blank)
Thanks for the reminder of the case statement. Old habits of using nested ifs dies hard :(
I would use a second field to display such text, or no field at all--just layout text that appears or disappears as needed via FileMaker 13's new "hide object when" setting or a conditional format if using an older version.