I am using *ngIf to show/hide the sidenav in the Angular version.  I noticed the "fixed-sn" class is being added to the main DOM element when the component is initialized, but it appears to leave it on the main DOM node when being destroyed.  I managed to fix this by doing the following:

constructor(private rd: Renderer2) { }

ngOnDestroy () { this.rd.removeClass(document.body, 'fixed-sn'); }

While this fixes my issue, I imagine other people will want this in the future.  Can this be incorporated into the Sidenav by default?