Unable to update CoursesPress Pro

I tried 3 times to update the plugin for version 1.3.4.1

1) from the WPMU Dashboard - i just get error "unnown error" in a red Notification bar
2) via the link in the list of plugins in the admin site - i just get error "unnown error"

3) via checkbox and batch operation (to see the process page of plugin update)
And just there i get a error message, that could help:

https://premium.wpmudev.org/api/dashboard/v1/download/913071/1560ffb3c3a50e028d9852b44ea2834fa3805868…

Cannot copy file: coursepress/includes/external/tcpdf/fonts/dejavusansmonob.z

Seems this file is missing somehow in the download? At least - it breaks the update process.

Please advise what to do...