Thanks Karl. I did not consider the cache. In the meantime, I ended up getting it to work going through a bunch of gyrations (ultimately creating a new temporary app and excel table with the same PtA content, getting that to refresh, then moving that worksheet back to my original spreasheet).
I will give the cache a shot if/when I encounter this issue again.
Just to wrap this up and hopefully help others, I ended up needing to create a new table within the Excel file that was causing me issues and even a brand new table would not refresh (I tried this after clearing the browser's cache).
SOLUTION: I ended up cut-and-pasting all the data from the various tables to a new Excel file, giving everything the same name so the app would recognize everything, and it worked fine.
Still, not an ideal solution and was very time consuming.
Anyway, hope this helps future readers of this thread.