Android build fails with App Flow

Dear community,

our Android build fails with App Flow. Does anyone know how to solve the problem? Thanks for any hints.

ionic Framework v5
Platform: Android
Build stack: 2020.11

Cordova CLI 10.0.0
Ionic CLI 6.12.1
Node.js 14.15.0
npm 6.14.8
Yarn 1.22.5
Debian 9.12
Gradle 4.3.1
OpenJDK 1.8.0_265

Build type: Debug

Logs:
[18:36:43]: Building android…
[18:36:43]: ▸ Error: Could not find or load main class org.gradle.wrapper.GradleWrapperMain
±---------------------------±----------------------+
| Lane Context |
±---------------------------±----------------------+
| DEFAULT_PLATFORM | ios |
| PLATFORM_NAME | android |
| LANE_NAME | android package_build |
| PROJECT_WEB_DIR | www |
| DOWNLOAD_CREDENTIAL_EXISTS | false |
| GRADLE_BUILD_TYPE | Debug |
±---------------------------±----------------------+
[18:36:43]: Shell command exited with exit status 1 instead of 0.
Error: Could not find or load main class org.gradle.wrapper.GradleWrapperMain

/usr/local/bundle/bin/fastlane: [!] Shell command exited with exit status 1 instead of 0. (FastlaneCore::Interface::FastlaneShellError)