android.enableR8.fullMode=trueにする場合でretrofit2、RxJava2を使う場合は下記のルールをproguardのルールに追加する必要があります。

https://github.com/square/retrofit/issues/3751#issuecomment-1192043644

 -keep,allowobfuscation,allowshrinking interface retrofit2.Call 
 -keep,allowobfuscation,allowshrinking class retrofit2.Response
 -keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation 

https://github.com/square/retrofit/issues/3774#issuecomment-1525677491

 -keep,allowobfuscation,allowshrinking class io.reactivex.rxjava3.core.Flowable 
 -keep,allowobfuscation,allowshrinking class io.reactivex.rxjava3.core.Maybe 
 -keep,allowobfuscation,allowshrinking class io.reactivex.rxjava3.core.Observable 
 -keep,allowobfuscation,allowshrinking class io.reactivex.rxjava3.core.Single