According to patch 6.5 notes, Blue/Red buff are intended to give 2 stacks.

They don't. For people who are confused and think that they mean it gave 2 stacks from blue/red buff when devourer was initially released: Devourer initial release in 4.20 (2 stacks from champ kills/assists, 1 from everything else): Sated devourer rework 5.13 (2 stacks from rift scuttler, 5 stacks from dragon/baron, 1 from everything else): It did not initially give 2 stacks from buffs, it never did. Just rift scuttler.
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