I think I understand why this error occurs.

I have

public class SomeClass : IValidate<ContentData>
{
    public IEnumerable<ValidationError> Validate(ContentData instance)
    {
        //I do EPiServer.DataFactory.Get(ContentReference contentLink) here
    }
}
  

I think, this method called before EpiServer load ContentProvider on first visit site in a long time, because if I delete "DataFactory.Get", error not repeated.

Is that so?