This failure matched Comment 1. Both failures have been on WebRender, so this is likely a WebRender bug (given that it's a graphical failure). Reclassifying.
Bug 1577770 Comment 7 Edit History
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This failure is the same style as the original one (as described in Comment 1). Also: both failures have been on WebRender, so this is likely a WebRender bug (given that it's a graphical failure). Reclassifying.