This morning I've had about 3 different uploads suffering from being 100% uploaded using the chunked uploader, but the failing with the error report invalid file key and appearing that I need to log in. However logging in does not seem to be the problem and the files are actually uploaded but missing the file upload comment (so the file history is an overwrite with a blank comment, something that may cause complaints against me later).

This may be a transient issue, or a known bug, but reporting just in case.

See attached screen shot from example https://commons.wikimedia.org/wiki/File:Lorenzo_Costa_-_De_heilige_familie.jpg