Did you check the hashes after?
You could try reflashing it by deleting the firmware and uploading it again. Alternatively, if there is sufficient room in the flash, delete the working image and then upload an older image and then the current one. The idea is to move the working image to a portion of the flash that isn't corrupt. Flash is soldered on these so without an SMD rework station it won't be an easy fix.
Thanks for your reply. It seems that my latest reply and your reply were within a few seconds of one another. It looks like my browser's cache was somehow interfering with the GUI behavior. I'm not quite sure how, but after flushing my browser cache, the issue was resolved.
Thanks for taking the time to reply and provide suggestions!
FWIW: I did check the file hashes and they were good matches.
Found a simple solution (that I should have tried already), but I'll leave the post up in case someone runs across the same issue.
Fix: Clear browser cache for any browsers used to access the GUI.
[As an aside: My problem wasn't associated with the flash access. I found that there were no problems there. After determining that the flash storage was okay, I decided to flush my browser cache. That did the trick.]