Ok. This is gonna be a stupid question that has got to have a right-in-front-of-your-face answer. So, here it goes ...
On one of my layouts, I have a set of tabs and on one of those tabs is a portal of related records. In the related table, I have a summary field that totals one of the fields. I am displaying that field on the tab, but outside the portal. But the pesky field is not showing anything. I can click into a portal field, then click outside the portal, and presto ... the total shows up. But as soon as I enter another portal row, the total disappears once again. Moving to another record, also shows a blank total (not zero, just blank).
I can open a separate window and view the raw table data and the summary field is populating just fine. I can have the data viewer open and the summary total shows just fine. It just doesn't want to show it's pretty face on my layout. And what burns me is, I've done this a bazillion times (well, not quite that many) and it has always worked.
Refresh window doesn't work. Refresh portal doesn't work. Refresh object doesn't work. Haven't tried a bigger hammer yet, but that is quickly becoming one of my next options. Or perhaps a cannon. Or maybe a bazooka.