In bug 1525603 Chris found that we have a problem with duplicates:
(In reply to Chris H-C :chutten from bug 1525603 comment #2)
Taking a closer look at the Dupes, only about two-thirds of them are fully dupes (ie, having the same docid). Over a third have different document ids.
We seem to have two different problems:
(1) full dupes with same document id, hinting at the fact that we might be sending dupes spread across a long time period or that the deduper on the pipeline is not catching them for other reasons;
(2) "half dupes", aka dupes with different document id, hinting at the fact that we have a problem in the SDK of re-using sequence numbers when we shouldn't