Original image file not always uploaded to S3 (but styles are)

[teeli]

I have this problem that occasionally some original image files are not saved to AWS S3. Most of the time everything works fine and it's maybe one file in 10000, but it happens semi-regularly (we currently have millions of files in S3, as stapler attachments, so it has happened quite a few times). What's weird is that some image styles are uploaded, but not the original. And it's not always the same styles, sometimes only one or two, sometimes everything but the original. This all seems to happen completely silently, since I can not find anything in any logs regarding the files. I haven't found any pattern for this and I'm not sure how to further test this. There doesn't seem to be any pattern to it.

So this is as much a bug report as it is an open question for any ideas that could help me better track down this issue to get to the bottom of it?