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When R8 full mode is enabled, it removes a constructor that is normally kept by Proguard. R8 without full mode keeps the constructor as expected. See Proguard rules and sample code below.

Proguard rules:
-keepclassmembers,allowobfuscation @com.example.reflectionerror.JobId class * {
    <init>(...);
}

Sample Application:
package com.example.reflectionerror

import android.app.Application

@Target(AnnotationTarget.ANNOTATION_CLASS, AnnotationTarget.CLASS)
@Retention(AnnotationRetention.RUNTIME)
annotation class JobId

@JobId
class Job

class App: Application() {
    override fun onCreate() {
        super.onCreate()
        try {
            Job::class.java.getConstructor()
        } catch (e: NoSuchMethodException) {
            throw IllegalStateException("No constructor")
        }
    }
}