Probably disabled logging in for server maintenance.
I haven't used iCloud backups on my iPhone, yet, I'm waiting for the GM version to be released first.
it's still in beta, it's not gonna work perfectly yet. the reason it's rejecting password is due to them messing with settings whilst it's in beta, it's to be expected. when they flick the switch for official launch, it should be fine. Apple have said in the release notes that during the beta period the cloud data could be wiped at any time, so not a beta glitch, it just means they're making improvements to it based on bugs found. you'd rather they didn't reset their servers during this testing period?? lol