RXJS 6.3.3 Ionic TypeError: Observable.combineLatest is not a function

Hello I have the problem that somehow I get this error in my Ionic Project:

rxjs_Observable__.Observable.combineLatest is not a function

im Using this Versions of RxJs:

"rxjs": "^6.3.3",
"rxjs-compat": "^6.3.3",

And the only time I use Observable is like this:

import { Observable } from 'rxjs';

Edit:

after debugging I can see the Error gets thrown on this line in my html:

<div ngxErrors="email" #emailErrors="ngxErrors">
  <div [ngxError]="['email', 'required']" [when]="['touched']" class="errorMessage">It should be a valid email</div>
</div>