For the past 24 hours my Pywikibot based upload projects have been receiving the error response:

empty-file: The file you submitted was empty.

Example upload failures from direct url upload white-listed sources are:

• https://tile.loc.gov/image-services/iiif/service:gmd:gmd411m:g4114m:g4114dm:g03985195001:03985_01_1950-0016/full/full/0/default.tif (147 mb) attempted 13:53 today (UK time)
• https://finds.org.uk/database/ajax/download/id/618971 (234 k) attempted 14:02 today.

Using a local cache and uploading from that appeared to make no difference, neither did uploading from my bot account. The local cache copies show there is nothing different about the files compared to previous batch upload runs from the same sources.

In the meantime, file overwrites using the same pywikibot upload module are working. Example https://commons.wikimedia.org/wiki/File:Tshi-zum-hau-kau_a_Winebago_LCCN2003670095.jpg at 13:33 today.