🐞 Bug report

Affected Package

@angular/animation or @angular/core

Is this a regression?

I've made a Stackblitz with Angular 9, 8 and 7. All versions have this problem.

Description

There is a problem when you nest a component with an :enter and :leave animation inside a parent which is conditionally visible using *ngIf. When the parent is visible for the first time there is no issue. Once you trigger the parent to leave and enter again, the child will not be visible.
It looks like the leave animation of the child gets triggered when the parent leaves but the enter animation isn't fired once the parent enters again.

🔬 Minimal Reproduction

I've made a simple example in Stackblitz. You can even make it less complex by removing the animations on the collapsible panel.
Stackblitz with Angular 17
Stackblitz with Angular 9
Stackblitz with Angular 8
Stackblitz with Angular 7

🌍 Your Environment

Angular 9 but it's also reproducible in 8 and 7.
Stackblitz contains my package versions.