Looking at the syslog it may be relevant, that this is a German installation.
I see:
Sep 20 23:07:17 ubuntu ubiquity: Bitte 'j' oder 'n' eingeben und Enter drücken
Sep 20 21:07:18 ubiquity: last message repeated 78 times
Maybe someone somewhere is passing a non-localized 'y' for 'yes' and someone else is expecting a localized 'j' (Ja for yes). Attaching syslog and debug log from ubiquity. This should have more info that the previous logs.
Looking at the syslog it may be relevant, that this is a German installation.
I see:
Sep 20 23:07:17 ubuntu ubiquity: Bitte 'j' oder 'n' eingeben und Enter drücken
Sep 20 21:07:18 ubiquity: last message repeated 78 times
Maybe someone somewhere is passing a non-localized 'y' for 'yes' and someone else is expecting a localized 'j' (Ja for yes). Attaching syslog and debug log from ubiquity. This should have more info that the previous logs.