The common denominator is your grinder.
Not if the RB works perfectly every time using the same grinder
But what's more likely?
It sounds weird and so for me, Occam's razor says it's the grinder.
Maybe next time you get a 'funny bean' get a mate to try grind it in their grinder and see what happens.
@Tenderloin started
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The common denominator is your grinder.