Sync Rule fails when trying to recreate Icinga object

When creating a sync rule for object import, the key column name from the parent Import Source is used as the ID during the matching phase. The key column name cannot be directly modified by adding a custom expression. Should this occur, you will see the following error:

This Sync Rule failed when last checked at 2019-01-15 09:35:08: Exception while syncing Icinga\Module\Director\Objects\IcingaHost linuxhost7.location: Trying to recreate icinga_host

To restore operation, you can either:

• Remove the modification to the sync property so the index is not customized

• Change the key column name to identify imported objects with a different unique key

• Use instead a new field created by an import source property modifier such as Combine multiple properties