I caved and git bisected. Looks like https://hg.mozilla.org/integration/autoland/rev/c3094bf072953ed649b5c81a9466508056e49803 is responsible for this (cannot believe I'm saying this). I'm verifying that reverting that commit fixes this on top of master.
Bug 1724298 Comment 14 Edit History
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I caved and git bisected. Looks like https://hg.mozilla.org/integration/autoland/rev/c3094bf072953ed649b5c81a9466508056e49803 is responsible for this. I'm verifying that reverting that commit fixes this on top of master.