This is happening when using client LoginWithCustomID, and may affect any "resurrected" account.
I frequently delete my test account and recreate it upon login, and I notice that this account has a different value for NewlyCreated than an account that has first login with a customID that has never been existed before.
Somehow, creating a new account from a customID that used to exist for a previously deleted account causes NewlyCreated to be false. I am unaware of any other means of determining whether this was a freshly created or resurrected account.
I use that bool to gate whether or not GetPlayerProfile gets called afterwards, since you can't call GetPlayerProfile on a NewlyCreated account. As an extra bit of information, GetPlayerProfile called when NewlyCreated is false on a resurrected account will fail with error 'ProfileDoesNotExist'.