How do hydraulic flat tappet lifters fail?

Well sports fans, the moment you've all been waiting for. Here's the cam and failed lifter. The lifter is worn down so badly that it was beginning to grind into the oil reservoir where the plunger is. Seeing this, I'm guessing the flattening lobe cause the lifter to decompress. What do you guys think about the other lobes?

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No doubt about it that lifter definitely failed because it was not rotating in the bore.
Either the bore was too tight and/or the cam lobe had no taper.