I'm not sure what you are doing to initiate the page refresh, but let's work with putting something like "location.refresh()" in an 'afterBoxEnd' callback.
The important thing to note is that floatboxes that start from a link in an iframe don't normally attach to that iframe's document. They attach to the parent or top document, as is evident from the fact that they visually display over the top document and are not confined to the boundaries of the iframe window.
So, running in the top window, a call such as "location.refresh()" will refresh that top window. To refresh an iframe's content from code running outside of that iframe, we first must get a reference to the iframe's window and then use the location object of that window.
First, put an id on the <iframe> element - it's easier to work with than a name.
Get a reference to the iframe element with
document.getElementById( 'theId') , or the simpler
fb.$( 'theId' ) function.
Once we have the iframe, it's window object can be found as the
.contentWindow property of that iframe.
And then of course having that window object, we can reference its location as the
.location property of that window.
Assembling those pieces together into an afterBoxEnd callback could result in something like this:
"afterBoxEnd:`fb.$( 'theId' ).contentWindow.location.reload()`"