React Native release apk doesn't match app when running react-native run-android

I'm currently building my first React Native app. I set up a release in Play Console for Internal Testing and was able to push my first signed apk. Since then, we've made bug fixes that are now merged into master. When I try to generate a new release by running:

cd android && ./gradlew assembleRelease

and upload as a new release, I don't see any of the new changes after updating my app via the Play Store.

I've tried running

react-native bundle --entry-file ./index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res/

before generating a new release, but I still don't see the changes.

Running react-native run-android while my device is hooked up with USB Debugging works fine, as well as in any emulator. I just can't figure out why my APK doesn't match the code generated on my local device.

Is there a step that I'm missing that's keeping my APK from representing the latest changes on master when I build?

Using React Native 0.56

Updated to add my Gradle Config:

 // android/app/build.grade
 signingConfigs {
    release {
        if(project.hasProperty('MY_RELEASE_STORE_FILE')) {
            storeFile file(MY_RELEASE_STORE_FILE)
            storePassword pass
            keyAlias MY_RELEASE_KEY_ALIAS
            keyPassword pass
        }
    }
}