I suppose that the Swing expression belongs to the Tempo Mark expression category, right?

Document menu > Category Designer…

In the Category Designer, highlight the Tempo Mark category, and examine the Score List.

What is selected in the Part column?

If there is more than one staff, go to the Expression window > Tempo Marks. Click on the Edit Categories button. In the next screen, where it says Score List 1, tap on the Edit... button to the right. Make sure that Check All Staves is checked. You will have to create your own Straight 8ths expression.

Ok, I'll try that. 

Thank you Mike Rosen! That fixed the problem! 

Glad I could help.

I'm doing a handbell piece with a swing rhythm. I'm using the expression tool > Tempo Marks, but it does not playback in swing. Any ideas to help? Thanks.

What is the time signature? Is it single staff, or two staves?

It would help if we could see the document. You can't post a finale doc here, but you could put it in DropBox, and post the link.

It's 4/4 on two staves. I don't have dropbox anymore, unfortunately. It did something to my computer.

Can you email it to me? wawoodman at icloud dot com

Did you receive the email?

I did, and just replied!

SOLUTION: Linda had edited the existing Swing expression to include a tempo mark. When she did that, the tempo playback overrode the swing. I started with a bare swing expression, and entered the tempo mark as a separate expression. After editing the Tempo Marks category to show on all staves (since Finale never fixed that) all was well.