Many 'Collision found on object property' errors leading to merge conflicts when upgrading to XWiki 12.10.3

STEPS TO REPRODUCE

1. Login to an older instance (e.g. 8.4.6 or 11.10.13)
2. Create a new subwiki
3. Close the instance
4. Go to the newer instance (12.10.3) and copy/cut the

   [...]webapps\xwiki

   folder and replace it (first delete the old one) in the same location on the older version

5. Start XWiki and follow the Distribution Wizard through the upgrade process
6. Go to Wiki Index and click on the previously created subwiki's name to start and run the DW for it

EXPECTED RESULTS

The upgrade process is completed successfully without errors both on the Main wiki, as well as on subwiki.

ACTUAL RESULTS

On Step 2 - Flavor, there are many errors encountered like:

Collision found on object property [...]

which lead to merge conflicts on the following pages:

• When upgrading from XWiki 8.4.6 to 12.10.3 (in no particular order):

  - XWiki.AttachmentSelector
  - Help.SupportPanel.WebHome
  - Help.TipsPanel.WebHome
  - Panels.Applications
  - Panels.DocumentInformation
  - Panels.MyRecentModifications
  - Panels.Navigation
  - XWiki.RegistrationConfig
  - XWiki.MessageStreamConfig
  - XWiki.UserDirectoryConfiguration
  - XWiki.UserProfileUIX
  
  - WikiManager.WikiUsers (only on subwiki)

• When upgrading from XWiki 11.10.13 to 12.10.3 (in no particular order):

  - Panels.DocumentInformation
  - XWiki.MessageStreamConfig
  - XWiki.Notifications.Code.NotificationsApplicationsPreferencesMacro

  When migrating from XWiki 8.4.6 to 12.10.3 (by resolving all merge conflicts automatically), the Dashboard entry is displayed twice in Applications Panel.

The issues could not be reproduced when upgrading to XWiki 12.10.2.