before this i also have same problem like u.. but the problem has gone after i unjailbreak my ip6+ for selling it.. it seems like before this i was messing up deleting one of the game app dominations keychain db file just to reset back for unbanned my acc , after that i notice i cant backup my data to icloud, .. I forgot to backup my file keychain.
after i unjailbreak to 9.3 from 9.0.2 my icloud can backup back normally...

and when I changed to a new phone ip6s+ and i was lucky to have 9.0.2 in it.. immediately i jailbreak and try to new backup.. so far no problem...
have u make any changes in ur keychain or related ??

nop kennot dahh... once apple stop singing then finish laa demm.... u can check here all the detail https://ipsw.me