FWIW I found the end of the installation.log
Starting job "grub" ( 38 / 40 )
.. Running QList("grub-install", "/dev/vda")
.. Target cmd: QList("grub-install", "/dev/vda") Exit code: 1 output:
Installing for i386-pc platform.
grub-install: error: unknown filesystem.
14:03:57 [1]: virtual Calamares::JobResult Calamares::Python::Job::exec()
ERROR: Error while running: CalledProcessError: Command 'grub-install /dev/vda' returned non-zero exit status 1.
At:
<string>(6): <module>
/usr/lib/calamares/modules/grub/main.py(46): install_grub
/usr/lib/calamares/modules/grub/main.py(63): run
14:03:57 [6]: virtual void Calamares::JobThread::run()
Skipping non-emergency job "gummi_entries"
.. Skipping non-emergency job "umount"
14:03:57 [1]: void Calamares::ViewManager::onInstallationFailed(const QString&, const QString&)
ERROR: Installation failed: "Bad main script file"
.. - message: "Bad main script file"
.. - details: Main script file /usr/lib/calamares/modules/grub/main.py for python job grub raised an exception.
14:03:57 [6]: void Calamares::ViewManager::onInstallationFailed(const QString&, const QString&)
Calamares will quit when the dialog closes.
14:03:57 [6]: DEBUG (Qt): Slideshow) deactivated
14:03:57 [6]: void Config::doNotify(bool, bool)
Notification not sent; completion: failed
14:06:02 [6]: void Config::doRestart(bool)
mode= "never" user wants restart? false force restart? false
Shutting down Calamares...
Finished shutdown.