After testing the iPadOS 17 beta since WWDC, I decided to start over fresh today and "Erase All Content and Settings" on my iPad. There were a couple of reasons for this. First, since iPad 17 beta 4, the Settings app wanted me to verify my recovery key for some reason, and I couldn't get rid of that warning. (FB12749748 for any Apple engineers in the audience.)
Thankfully, that warning is gone now after the erasure. Second, I was still experiencing a bug left over from the iPad 16 beta in 2022 that prevented me from successfully dragging and dropping any apps into the Dock after having removed all of the apps from the Dock except Safari. (FB11749674) Thankfully, that issue is also gone now after the erasure.
I discovered to my dismay that after erasing all content and settings, I had to connect the iPad to a Mac and let it phone home to Apple in order to "activate", but that's a story for another day. The story here is that I had a lot of trouble signing the iPad into iCloud, because the two-factor authentication codes kept disappearing! When you sign in to an Apple service with your Apple ID on one device, Apple sends authentication codes to all of your devices that are already signed in with your Apple ID. (This may include the very same device, if it's already signed in to another Apple service.) The problem was that the 2FA dialog briefly appeared on the screen of my Mac and then disappeared before I could read it or get the code! This happened repeatedly. I tried with another one of my Macs, and the same problem occurred there too.
I remembered that I had experienced the same problem back in July signing in to iCloud on a Mac running Sonoma beta 4, though there were also crashes involved, i.e., the AppleIDSettings process was crashing. (FB12746765) So of course I searched the web for this problem, and I found a number of references in Apple's discussion forums, for example: https://discussions.apple.com/thread/254543268 (2023), https://discussions.apple.com/thread/253537191 (2022), https://discussions.apple.com/thread/252422074 (2021), https://discussions.apple.com/thread/251633683 (2020), https://discussions.apple.com/thread/250287891 (2019), https://discussions.apple.com/thread/250457936 (2019). Unfortunately, however, there were only questions, no answers or solutions.
Eventually I gave up and had Apple send me a 2FA code to my phone number via SMS, and that worked to sign in my iPad to iCloud. Nonetheless, I still wonder what in the world is going on, and how many other people in the world are experiencing the same problem. I'm blogging now to raise awareness of this, and hopefully get Apple's attention. I haven't had much luck lately getting Apple's attention via Feedback.