Issue while migrating config from 4000s to r4600

No, the issue you mentioned is related to the master key of the iSeries device, as you stated. My post was simply to add useful information to help complete the backup restore process.

In my experience, when a restore failed with the error "Symmetric Unit key decrypt failure - decrypt failure, configuration loading error: high-config-load-failed," we recreated the tenant, copied the master key using f5mku -r <key value>, rebooted the tenant, and then executed the UCS restore.