Errors when upgrading from an older version of XWiki containing sub-wikis

Prerequisites: An instance of an older version of XWiki (e.g. v 8.4.5) containing at least one sub-wiki and a newer version (to which will be migrated - e.g. v 9.6) are available.

STEPS TO REPRODUCE:

1. Delete the "data" folder from the newer version
2. Copy the "data" folder from the older version and paste it in the folder of the newer version
3. Start XWiki
4. Login as Admin
5. Use the Distribution Wizard to complete the upgrade process
6. Observe the install log

EXPECTED RESULTS

The upgrade to the newer XWiki version (e.g. v 9.6) is successfully completed without any errors.

ACTUAL RESULTS

When installing the standard flavor, some errors/warnings appear in the install log (screenshot attached), regardless of the configured database (HyperSQL, PostGreSQL, MySQL or Oracle).