#ngrx/store-devtools - effects called twice - angular6

Question

All actions I dispatch in effects are called twice. I already figured out, that this is caused by StoreDevtoolsModule. When I kick StoreDevtoolsModuleout of the app.module.ts my action will be called only once => everything is fine.
Here's my setup:
Angular 6.0.1
"#ngrx/effects": "6.0.0-beta.1",
"#ngrx/entity": "5.2.0",
"#ngrx/router-store": "6.0.0-beta.1",
"#ngrx/store": "6.0.0-beta.1",
"#ngrx/store-devtools": "6.0.0-beta.1",
app.module.ts
import { BrowserModule } from '#angular/platform-browser';
import { StoreModule, Store, combineReducers, ActionReducerMap, MetaReducer }
from '#ngrx/store';
import { StoreDevtoolsModule } from '#ngrx/store-devtools';
import { EffectsModule } from '#ngrx/effects';
import { EquipmentModule } from './modules/equipment/equipment.module';
const reducers: ActionReducerMap<IAppState> = {
equipments: EquipmentReducer
};
#NgModule({
declarations: [
AppComponent
],
imports : [
BrowserModule,
StoreModule.forRoot(reducers),
StoreDevtoolsModule.instrument({
name: 'EQUIPMENT',
maxAge: 10,
logOnly: true,
}),
EquipmentModule,
EffectsModule.forRoot([]),
]
})
export class AppModule
{}
equipment.module.ts
import { EffectsModule } from '#ngrx/effects';
import { EquipmentEffects } from './equipment.effect';
import { EquipmentMockService } from './equipment.mock';
#NgModule({
imports: [
EffectsModule.forFeature([EquipmentEffects])
],
providers: [
{
provide: 'IEquipmentService',
useClass: EquipmentMockService
},
]
})
export class EquipmentModule {
}
equipment.effect.ts
import { CustomAction } from './../../custom.action';
import { Injectable, Inject } from '#angular/core';
import { Http } from '#angular/http';
import { Actions, Effect, ofType } from '#ngrx/effects';
import { Observable } from 'rxjs/Observable';
import { catchError, map, mergeMap } from 'rxjs/operators';
import { EquipmentActions } from './equipment.action';
import { HttpClient } from '#angular/common/http';
import { Action, State } from '#ngrx/store';
import { of } from 'rxjs/internal/observable/of';
import { EquipmentService } from './equipment.service';
import { IAppState } from '../../app.state';
import { ofTypeWithPayload } from '../../customActionHelper';
#Injectable()
export class EquipmentEffects {
constructor(
private http: HttpClient,
private actions$: Actions,
private readonly state: State<IAppState>,
#Inject('IEquipmentService')
private equipmentService: EquipmentService
) { }
#Effect()
getAllEquipments$: Observable<Action> = this.actions$.pipe(
ofType(EquipmentActions.LOAD_ALL_EQUIPMENTS),
mergeMap(action => {
console.log('here'); <-- This console.log gets called twice!
return this.equipmentService.getAllEquipments().pipe(
map(equipments => ({ type: 'LOAD_ALL_EQUIPMENTS_SUCCESS', payload: equipments })),
catchError(() => of({ type: 'LOAD_ALL_EQUIPMENTS_FAIL' }))
);
}
)
);
Does anyone have an idea?
Thanks