Document is missing attachment

A user posted 4 files. We create a separate doc with 1 attachment for each file. We did so with a single POST to bulk_docs. SG returned an array with 4 ok:true. 3 docs had uploaded correctly, while 1 doc is missing attachment:

GET /db/cj4oog40m0004w2jxoq87x2vr
"_attachments": {
“image.jpg”: {
“content_type”: “image/jpeg”,
“digest”: “sha1-lwqSF7199a9fdA4tJDCijLNmrzs=”,
“length”: 2206090,
“revpos”: 1,
“stub”: true
“channels”: [

"_rev": “1-a8d7b4e4745b6d3eb73d05c2d5449b02”,
"_id": “cj4oog40m0004w2jxoq87x2vr”

GET /db/cj4oog40m0004w2jxoq87x2vr/image.jpg

There is no _sync:att:sha1-lwqSF7199a9fdA4tJDCijLNmrzs= doc in the DB.

This happened twice in two days. We have less than 10 users currently so that is rather high rate.
First time we thought it has to do with a network issue, as client was remote PouchDB and first two docs were uploaded immediately and correctly, 3rd had uploaded immediately but broken, and 4th had uploaded correctly after 2 hours.
Second time client was a service running on the same server and all 4 docs were uploaded at once.

We were not able to reproduce this artificially.

What could be the cause? Is there a way to force a client to re-replicate the doc?

Thank you.

@andy, @traun: does this ring a bell?