If the upgrade has failed for one or more devices, there are several methods of error diagnosis:

Look at the output of the IGEL Linux 10 Upgrade Tool after the fallback to IGEL Linux v5 has been completed.

Go to > System > System Log Viewer and look at the /var/log/messages entries for the current day.

If the device has booted into the Linux 5.11 rescue system, you can find debug information in /wfs/igel_v5_to_v10_migration.log