iCloud is unwanted and obnoxious, always turning itself on immediately and without asking, causing no end of issues.
That said, here's the history and the solution to how I got rid of this latest pointless and unwanted and UNintuitive ("it just works" definitely died with Steve!) "Some icloud data isn't syncing" on an iPad...
1) Got a new iPad and created a *new* Apple ID on it, and turned everything for iCloud Off on this iPad
2) Used this same (new) Apple ID to log into an old iPhone and also turned Off all of the iCloud junk on that too, but that's when the iPad got this ridiculous message
3) I fianlly just clicked the "Resume Synching" (or whatever?) link for that alert, and waited waaaay too long for it to do something and the iPad eventually asked for the passcode for the iPhone (what?!).
4) Once I entered the iPhone's passcode on the iPad (WHY, APPLE, WHY?! Just b/c a bunch of ding-dong celebrities were dopey enough to let their pics get loose b/c they are even bigger bozos than Apple is these days, now the whole world gets this obnoxious and overly onrous and incestual security nonsense on your devices?)
Now, the alert is gone from the iPad and both the iPad and the iPhone have everything re: iCloud as Off, as it should be by default.
NOTE: Turning iCoud on w/o even asking and forcing users to scour for all of the settings and rushing to turn it all off before data is auto-vacuumed into the cloud should be illegal!