I am using ArcGIS Pro to update some of our old poster maps. I am trying to dynamically label individual detail maps on the poster. I have a title for each of the detail maps in a "rectangle text" item. I'd like the text in this item to be vertically centered. Based on the Format Text dialog, this seems to be possible. In fact, it works for regular text, say with a marker background, but not for rectangle text items. Am I missing something?
oh.. OK well I am currently testing a development version of ArcGIS Pro (2.3) and it appears to be working... so perhaps a bug in your version.
You do have to click the Apply button to see it change in the layout.
In the meantime, you can use Offset X and Offset Y to position text within the rectangle. Unfortunately, you'll need to make adjustments for each text element based on size of rectangle and text string.