Why is ngOnInit called twice?
Why it is called twice
Right now, if an error happens during detecting changes of content/view children of a component, ngOnInit will be called twice (seen in DynamicChangeDetector). This can lead to follow up errors that hide the original error.
This information comes from this github issue
So it seems that your mistake might have an origin elsewhere in your code, related to this component.
This was happening to me because of a faulty component html. I had forget to close the selector tag in the host component. So I had this <search><search>, instead of <search></search> - take note of the syntax error.
So related to @dylan answer, check your component html structure and that of its parent.