No one has mentioned this above, maybe because it's rather common knowledge about Reinhardt, but he's the judge who, when asked about his decisions being so frequently overturned by SCOTUS, bragged “
They can’t catch them all.”
https://www.nationalreview.com/bench-memos/this-day-in-liberal-judicial-activism-december-30/Stephen Reinhardt. The Ninth Circuit arch-activist who has made a career of defying the Supreme Court—“They can’t catch them all,” he boasts of his wayward rulings—purports to take offense that a dissent from the denial of rehearing en banc in Belmontes v. Ayers (see This Day for June 13, 2008) implies that his rulings in that case have “flouted the will of the Supreme Court.” Some eleven months later, in a unanimous per curiam opinion (in Wong v. Belmontes), the Supreme Court summarily reverses Reinhardt—
the third time in this same case that the Court has reversed or vacated one of his rulings. Further, the Court states that it finds his reasoning incomprehensible and fanciful, and it notes his manipulative recharacterization of the evidence.
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In the OP case being discussed, the publication of the opinion was illegal because until the moment of publication any judge partaking in the case can change their mind and alter their vote or the written opinion if they wrote it (and Reinhardt wrote this one). Obviously if a participating judge is dead at some point prior to the publishing of the opinion, they are no longer able to exercise their option to change their vote or written words, thus invalidating the final opinion.