It seems surprising to me that this kind of basic thing (does the update work on the hardware we've released) wasn't validated by Apple prior to releasing this software update. Perhaps a sign of issues in the QA process at Apple around MacOS?
Release candidate was up on the developer site for a week and another comment says that only a subset of people are having the problem . It would seem that the group is some kind of anomaly that never got a release candidate installed also.
There can be outlier bugs, that only appear for a small subset of users, under certain conditions (from different OEM parts combo among dozens to different software packages installed, update paths followed, or options enabled).
From what the article says, this is specifically a problem when updating from an OS version released two days ago, to the other OS version released two days ago. That's not exactly the most logical or likely path for most users to take, though obviously Apple needs to be able to handle this going forward for users who are hesitant to update to 26 and want to run 15.7 in the meantime.
Of course not. But it makes sense that a bug with a narrower scope is more likely to escape testing, and apparently something that changed between 15.6.1 (released a month ago) and 15.7 (released two days ago) affects the process of upgrading to 26. So whatever code is at fault is probably pretty recent.
