Android Studio 3.5.3
Build #AI-191.8026.42.35.6010548, built on November 15, 2019
JRE: 1.8.0_202-release-1483-b03 amd64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0

My Cast app stopped working some time after upgrading Android Studio 3.5 to 3.5.x (haven't tested my app since 3.5.0). I did not change anything in my code, except updating some libraries (including Cast). I decided to rebuild my app and re-test it. Now, when I press the Cast button, it crashes. But only in Release mode, so I'm quite convinced that it is related to R8.

As can be seen below, some object "com.google.android.gms.internal.cast.zzka" seems to be null. The exception (after some manual re-mapping) tells us this:

java.lang.NullPointerException: Attempt to write to field 'boolean com.google.android.gms.internal.cast.zzka.zzbio' on a null object reference

I'm using the latest version of the Cast Framework, but I verified the bug in 17.1.0 too.
implementation 'com.google.android.gms:play-services-cast-framework:18.0.0'

And in my manifest.xml:

<meta-data android:name="com.google.android.gms.cast.framework.OPTIONS_PROVIDER_CLASS_NAME"
android:value="com.myapp.CastOptionsProvider" />

Targeting SDK v29. I have enabled R8 full mode, but disabling it does not fix the problem. Since there were no relevant code changes since Android Studio 3.5 I'm suspecting one of the minor updates to be the culprit. Perhaps something was changed in R8?

Here are some relevant entries from the mapping file:

com.google.android.gms.internal.cast.zzka -> c.c.a.b.h.b.h5:
boolean zzbio -> b
...
com.google.android.gms.internal.cast.zzmd -> c.c.a.b.h.b.z6:
1:1:void <init>():0:0 -> <init>
1:1:void <init>(com.google.android.gms.internal.cast.zzmb):0 -> <init>
1:1:void com.google.android.gms.internal.cast.zzka.zzhx():0:0 -> a
com.google.android.gms.internal.cast.zzms -> c.c.a.b.h.b.m7:
com.google.android.gms.internal.cast.zznw zzbpg -> j
java.lang.Object[] zzbot -> b
com.google.android.gms.internal.cast.zzba -> c.c.a.b.h.b.s:
com.google.android.gms.internal.cast.zzav zzng -> a
com.google.android.gms.cast.framework.zzag -> c.c.a.b.c.x.c0:
com.google.android.gms.cast.framework.SessionManagerListener zzlo -> a
com.google.android.gms.internal.cast.zza -> c.c.a.b.h.b.a:
com.google.android.gms.internal.cast.zzaq -> c.c.a.b.h.b.i:
com.google.android.gms.cast.internal.Logger zzu -> b
com.google.android.gms.internal.cast.zzag zzmt -> a
androidx.mediarouter.media.MediaRouter$GlobalMediaRouter$CallbackHandler -> b.p.n.s:
androidx.mediarouter.media.MediaRouter$GlobalMediaRouter this$0 -> b
java.util.ArrayList mTempCallbackRecords -> a

And the entire exception:

java.lang.NullPointerException: Attempt to write to field 'boolean c.c.a.b.h.b.h5.b' on a null object reference
at c.c.a.b.h.b.z6.a(:1)
at c.c.a.b.h.b.m7.b(Unknown Source:48)
at c.c.a.b.h.b.d6$a.f(:3)
at c.c.a.b.h.b.d6$a.g(:1)
at c.c.a.b.h.b.u.a(Unknown Source:4)
at c.c.a.b.h.b.s.a(:19)
at c.c.a.b.c.x.c0.a(:18)
at c.c.a.b.h.b.a.onTransact(Unknown Source:22)
at android.os.Binder.transact(Binder.java:914)
at jx.b(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):14)
at vx.a(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):39)
at wj.b(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):50)
at wk.a(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):42)
at wv.c(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):21)
at wt.a(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):11)
at jy.onTransact(:com.google.android.gms.dynamite_dynamitemodulesc@19831081@19.8.31 (120400-0):5)
at android.os.Binder.transact(Binder.java:914)
at c.c.a.b.h.b.r.b(Unknown Source:7)
at c.c.a.b.h.b.i.d(:4)
at b.p.n.s.a(:2)
at b.p.n.s.handleMessage(:6)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

I'll try to pinpoint the error even more. Perhaps I will somehow be able to reproduce it in a sample project. But please give me some hints. What could have gone wrong just by updating Android Studio?