Also, looking at the stack logs it seems like both versions include version 6.3 of Gradle, so I don’t think the build problems are caused by this.
For 16.04: bitrise.io/linux-docker-android.log at master · bitrise-io/bitrise.io · GitHub
For 20.04: bitrise.io/linux-docker-android-20.04.log at master · bitrise-io/bitrise.io · GitHub