Stacktrace TITLE in Firebase Crashlytics isn't deobfuscated

### [REQUIRED] Step 2: Describe your environment

* Android Studio version: 4.1.2
* Firebase Component: Crashlytics
* Component version: com.google.firebase:firebase-bom:26.2.0

### [REQUIRED] Step 3: Describe the problem

#### Steps to reproduce:

We have an android app in production and we use the Firebase Crashlytics.
Everything is good on Firebase Crashlytics page. The crashes stacktrace is deobfuscated. Only the stacktrace TITLE isn't deobfuscated. Look at the screenshot http://prntscr.com/xm0g6s .
How to show human-readable TITLE? Why stacktrace is deobfuscated but title isn't? Seems it s a bug.

#### Relevant Code:

Dependencies I used:
```
implementation platform('com.google.firebase:firebase-bom:26.2.0')
implementation 'com.google.firebase:firebase-messaging'
implementation 'com.google.firebase:firebase-analytics'
implementation 'com.google.firebase:firebase-crashlytics'
```

ProGuard is ON in the release build. My proguard-rules.pro file: https://gist.github.com/SergeyKharuk/f7bc59c328662fd39232c80bfd87eba8