See issue #2331. Timestamp is expected in format yyyy-mm-dd (plus other information), with the expectation that month and day are 2 digits zero-filled on the left if needed. The user's file instead used a space rather than zero as filler. Although I don't know how the unexpected timestamp was created, it was easy enough to alter the timestamp in an otherwise normal spreadsheet, and use that file as a test case.
oleibman