My kids iPad has been doing the same. It keeps saying we're locked out, and not accepting the (correct) password, and we have to reset the password constantly. No idea why it's happening. I've tried setting simpler passwords (I use KeePass and generate 32char complex passwords by default), but it doesn't help. I never thought of the fact that it could be someone brute forcing it and locking us out, I just shrugged it off as being "typical new-Apple". We're almost completely off Apple devices now because we have so so many problems with them in the last couple years, after being a happy Apple family since the Macintosh SE.