The pratfall on the reboot after the update *would* point towards an underlying issue, or that might only be a terribly unlucky coincidence (because, well, the dummy package does what it says on the tin, i.e., nothing permanent. If it were to cause an issue, that would be during the update process itself).
Barring that, no clue. worksforme, and, AFAICT, you're not doing anything wrong.
Out of curiosity, how old is the device, are you its first owner, and do you know if untowards things were ever done to it?
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