Comment by anon7000
Bingo. My wife’s phone failed to backup to iCloud. To be fair, there’s an error message. However, the list of what takes up space does not show what’s actually taking up space. Such as videos texted to or from you (can easily be multiple gigs as they add up over a year or two)
The list didn’t show the god damn GoPro app, which was taking up 20GB of space from downloaded videos. I guessed it was the problem because it showed up in the device storage list, but literally not reported when you look at the list of data to backup.
iMessage is another great example of a failure. I changed my iMessage email and didn’t receive messages in a family group chat until I noticed — I had to text the chat before stuff started coning through. Previously sent messages were never delivered. And they all have my phone number, which has been my primary iMessage for LITERALLY over a decade. iMessage’s identity system is seriously messed up on a fundamental level. (I’ve had numerous other issues with it, but I’ll digress.)
It’s messed up, but it can be fixed by turning off iMessage and MMS in settings.app and then turning it back on. It’s an old bug. Since it hasn’t been fixed, I’m guessing the solution introduces more problems than it a solves for whatever reason.