There’s been a lot of stories in the news the past few days since the Windows 10 Anniversary Update went live of people running into issues with unexpected hangs and blue screen crashes after the update (for example). Even the update itself does not seem to be as smooth as it could have been.
On my HP desktop, I went through the first few reboots during the upgrade and then got stuck at a gray screen with the rotating progress balls. There was some disk activity every couple of seconds so I left it running, checking back on it every hour or so, but it stayed at this point for a whole day. Thinking it had just hung, I rebooted it and got a ‘Recovering your installation’ message, and then it seemed to pick up again at the “Working on Updates” progress screen. After about another 15mins and sitting at 91% complete, there’s a ton of disk activity so I’ll leave it running and check back on it later today.
If you’ve run into other issues during the upgrade, there’s a list of commonly seen issues so far in this article that might be useful.