I am receiving the following strange dependency injection behavior when using custom HttpInterceptors in angular 5+.
The following simplified code works fine:
Angular Team resolved this issue in Angular 5.2.3 released 31 January 2018. After updating angular version you will be able to inject services that use HTTPClient as normal in constructor
Bug Fixes
common: allow HttpInterceptors to inject HttpClient (#19809) (ed2b717), closes #18224
from Angular changelog