Inline CSS from Angular Animations lost when reattaching Route Snapshot

[IanNMarshall]

🐞 bug report

Affected Package

@angular/animations
@angular/router

Is this a regression?

Behavior started with angular 9

Description

When using a Custom Route Reuse strategy the css that had been applied via an angular animation disappears leaving the element in neither "animation state"

🔬 Minimal Reproduction

https://github.com/IanNMarshall/angular9-animations-example

Steps to reproduce

$ ng serve

1. Click the "animation" button to be routed to /animation
2. Toggle the animation any number of times or none at all
3. Click home to navigate away
4. Click "animation" again and the animation css has been removed, it is in neither the open or closed state.
5. Additionally if you now toggle the animation it works for all future routing

Working example

Same src as above example but pre angular 9, works as expected, keeps animation state.
https://github.com/IanNMarshall/angular8-animation-example

🌍 Your Environment

Angular CLI: 9.1.0
Node: 12.13.0
OS: darwin x64

Angular: 
... 
Ivy Workspace: 

Package                      Version
------------------------------------------------------
@angular-devkit/architect    0.901.0
@angular-devkit/core         9.1.0
@angular-devkit/schematics   9.1.0
@schematics/angular          9.1.0
@schematics/update           0.901.0
rxjs                         6.5.4

Anything else relevant?
Could not mimic this behavior with [style] binding or setAttribute("style") seems to only happen with animations.

[matsko]

Hello @IanNMarshall. I can definitely see the issue here, but it's not yet clear whether or not this is caused directly by animations or from the router/core part of the framework. In other words, we need to investigate more. I've added the labels here so that we can track this issue and once we have more time fully get to the bottom of it. Thank you for reporting this.

[Da13Harris]

Seems like #26133 and #35270 might be related to this. Ivy + animations + custom RouteReuseStrategy = broken.