I’m starting to see some commonality now, with the symptoms you describe.
For example, in the Stable Update Announcement thread:
At this time it’s no doubt difficult to see the cause, however I suspect that older machines and poor maintenance might generally be among the contributors to the problem.
This is only supposition on my part.
However, at least one post I’ve seen in the thread indicates that the user’s system was in an “unsupported state” before they thought it was a wonderful idea to update. Plus, they seemingly hadn’t bothered to read through Known Issues and Solutions before updating.