In bug 1071577, we switched away from using &pushID=N when polling json-pushes, to using json-pushes with &maxhours=24. Unfortunately maxhours is not a valid param, so we're effectively using json-pushes with no start params at all, which means we're requesting the last 10 pushes made to each repo. This increases network transfer & processing costs, and also means that if there were more than 10 pushes since the last successful poll, we'd miss pushes. (10 pushes in a few mins is unlikely in normal operation, but if ingestion went down for 15-20+ mins, there's a chance we might hit it, given push rates at peak times). As an added bonus, using &fromchange doesn't have the same pitfalls as pushID - in that we correctly get a 404 if the repo was reset (ie bug 1065771 doesn't apply). eg: https://hg.mozilla.org/mozilla-central/json-pushes?full=1&fromchange=invalid
This is now happening as part of bug 1072291.