Oh, forgot, the 3.3MB JPG upload was attempted on both Artwork and Photos; both of these failed.

I just did two more tests. I attempted to upload a 1MB PNG via "Photos" and it worked. I attempted to upload that same image (a 1MB PNG) via Artwork, and is ALSO succeeded! I then attempted to upload a 3.3MB JPG, and it once again hung. Possibly a size issue, despite these being well under the allowed limit?