On Thu, Sep 17, 2020 at 01:06:50PM +0200, Ævar Arnfjörð Bjarmason wrote:

The reason is detailed in [1], tl;dr: empty loose object file issue on
ext4 allegedly caused by a lack of core.fsyncObjectFiles=true, but I
didn't do any root cause analysis. Just noting it here for for future
reference.

All the modern Linux file systems first write the data, and then only
write the metadata after the data write has finished.  So your data might
have been partially or fully on disk, but until the transaction to commit
the size change and/or extent state change you're not going to be able
to read it back.