Firestore listener freezes Unity Editor on second launch (works on 6.15?)

[scascar]

[REQUIRED] Please fill in the following fields:

• Unity editor version: 2019.4.14
• Firebase Unity SDK version: 6.16.1 . Then downgraded to 6.15.2 and it worked
• Source you installed the SDK: Package manager
• Problematic Firebase Component: Firestore (DocumentReference.Listen)
• Other Firebase Components in use: Auth, Storage, Functions
• Additional SDKs you are using:
• Platform you are using the Unity editor on: Windows
• Platform you are targeting: Android
• Scripting Runtime: IL2CPP

[REQUIRED] Please describe the issue here:

Hello, so I spent the last 5hours trying to resolve this bug, and the only way for me was to downgrade the sdk to 6.15.2.
This happened the first time i used the listener for firestore. On the first run, everything runs smoothly, but if i try to recompile or restart the project a second time, the editor hangs indefinitely.
The issue the closest to mine was #638 .
Seeing that there was a fix for 6.15.1, i gave it a chance, downgraded to 6.15.2 and apparently that solved my issue.

The editor logs were frozen on “Begin MonoManager ReloadAssembly”.
Sorry if thats not very detailed, I tried so many things ask me any question for explanation.

Steps to reproduce:

Have you been able to reproduce this issue with just the Firebase Unity quickstarts (this GitHub project)? No I used an existing firebase project.
What's the issue repro rate? 100%

What happened? How can we make the problem occur?
Just call a .Listen on a DocumentReference, quit play mode and try to restart.

Relevant Code:

//Basically call this anywhere in the project, on an existing DocumentReference object.
docRef.Listen(snap => TestFunc());

[dconeybe]

Unfortunately, this is a known issue and a fix is actively being worked on. Please see #845 for full details and a suggested workaround. I'm going to close this issue since it looks like an exact duplicate of #845, but feel free to re-open if you feel that it is a distinct issue.