When Updating a user’s profile for an application, attributes that are set via mapping can not be updated this way.
For example any of the attributes on the Okta User Profile. Those must be updated via called to the User API - Update User.
In my case I was trying to set a user’s preferred timezone.
I think the documentation should mention this.
You might want to send a warning for calls to APP API - Update Application Profile for Assigned User, that try to update a mapped attribute.