Apparently, don't EVER change your AppleID password, or it will totally f-up everything. Tonight, I decided to change my password as I'd recently sold a couple of old devices and, although I did a full wipe/reset on all of them, I guess I was just being careful. So, I did it through the iForgot system. Everything went as expected, had to sign back into iMessage, iCloud, etc. So, later on, a message pops up on my Mac Mini: "Your iCloud Keychain was reset". Huh? Ok, I clicked it and it said I either had to authorize it from another device, or use my code. Um, ok...I use it on my iPhone and iPad, so I said to authorize. Nothing. No notifications on the other devices. I went into Settings on my iPhone, and it was turned off. Huh? Ok...I don't know how that happened, but I turned it on. Told me "iCloud keychain was reset" and I had to reauthorize. Great. Went through the code thing, and it seemed like it turned it on. Went back to my Mac, did the "authorize" thing again, waited for the message. Instead of getting the request to authorize, my iPhone said "your iCloud keychain was reset". So I decided to forget the iPhone for now and focus on the Mac. I've been trying for 2 hours, have done the code-based reset countless times. Each time, it works, keychain is enabled for about 5 minutes and then I get the "your iCloud keychain was reset". I have no idea what to do next. I have found very few accounts of this on the support forums. I guess I'll have to open a ticket or something, but I don't even know what device to say I'm having trouble with.