Working fine on GAE using your demo but my script has the following ...

[gotye78]

I don't understand what could be different between yours and mine ...

2019-09-27 12:10:59 default[20190927t200756] EasyProcessCheckInstalledError(<EasyProcess cmd_param=['Xvfb', '-help'] cmd=['Xvfb', '-help'] oserror=[Errno 2] No such file or directory: 'Xvfb': 'Xvfb' return_code=None stdout="None" stderr="None" timeout_happened=False>) 2019-09-27 12:10:59 default[20190927t200756] cmd=['Xvfb', '-help'] 2019-09-27 12:10:59 default[20190927t200756] OSError=[Errno 2] No such file or directory: 'Xvfb': 'Xvfb' 2019-09-27 12:10:59 default[20190927t200756] Program install error!

[balsammmmmmmm]

Same