Q: Can't resolve all parameters for BreakpointsService Upgraded from Angular 5.2 to 6.0 and got the above warning
Can't resolve all parameters for BreakpointsService in node_modules/angular-breakpoints/index.js This will become an error in Angular v6.x

A: It seems that this library is out of date (last commit ~1.5 years ago) and not compatible to Angular versions >= 5.2. The Github repo is also marked as archived.
You might want to have a look at the @angular/cdk layout module, which offers similar functionality.
Example for running code in case the viewport is Medium or Large, using @angular/cdk:
export class AppComponent implements OnInit  {
    constructor(public breakpointObserver: BreakpointObserver) {}

    ngOnInit() {
        this.breakpointObserver
            .observe([Breakpoints.Medium, Breakpoints.Large])
            .subscribe((state: BreakpointState) => {
                if (state.matches) {
                    console.log('medium or large');
                    // do sth.
                }
            });
    }
}

