Here you can find typical upgrade failures and the appropriate methods to regain a usable system.
Device Has Upgraded to Igel OS 11, but Does Not Boot Any More
To get a working IGEL OS 11 system:
IGEL OS 10 Rescue System Fails to Update Missing Partitions
If a severe error has occurred during the upgrade process, the device boots into a minimal 10.05.700 (or higher) rescue system. If unattended, the device tries to download and update the missing partitions and reboots on failure.
To regain a full IGEL OS 10 system, you have two possibilities:
In the rescue system, start the Setup, go to System > Update > Firmware Update and set a valid update source for the appropriate IGEL OS 10 firmware version (10.05.700 or higher).
Configure a UMS profile that contains a valid update source for the appropriate IGEL OS 10 firmware version (10.05.700 or higher) under System > Update > Firmware Update and assign it to the device.