If you click into the cell in Excel, do you then see all the values. What you have in FileMaker appears to be a list of values separated by returns? I'm not sure how that will export to Excel.
You may want to define a calculation field like this: Substitute ( Lists ; ¶ ; ", " ), then export from this calculation field in place of the original text field. This will format the data into a horizontal row separated by commas which may be easier to see in the spreadsheet.
Or is it a portal? In which case you could List (relationship::Category). Excel seems to handle the return-separated OK (much the same as FileMaker does), though it can show them on the same line. If you double click within the cell, it would resize the row to show as separate lines; at least on Mac Excel 2011.