It is really strange. I've done this now multiple times, always with the same result. The upgrade yields the warnings and errors above. Rebooting after the upgrade - and that is really curious - works once. I can log in and do whatever i want, but when i reboot a second time (counting from the last upgrade), the system hangs with the blue alive LED being continuously on (which looks like no kernel is booting at all - at least there is no output on the screen). /var/log/messages also says that no system has been started. dd'ing the image Armbian_5.14_Odroidc2_Debian_jessie_3.14.72 again and everything is fine, so it doesn't look like a hardware error?