Não consegui usar o ngClass, pois, retorna o seguinte erro de compilação:
Error: src/app/shared/components/loading/loading.component.html:11:5 - error TS2322: Type 'string | null' is not assignable to type 'string | string[] | Set<string> | { [klass: string]: any; }'.
Type 'null' is not assignable to type 'string | string[] | Set<string> | { [klass: string]: any; }'.Então, optei por fazer desta forma:
<div *ngIf="(loading$ | async) == 'loading'; then loading; else stopped"></div>
<ng-template #stopped>
<hr class="stopped"/>
</ng-template>
<ng-template #loading>
<hr class="loading"/>
</ng-template>
:.( snif
