SCCM Content Conversion not showing Packages when reassigning DP

Symptoms :
SCCM Administrators tries to Upgrade/Reassign a distribution point in a migration project. The Content Conversion tab is displaying There are no items to show in this view. This blog post will show how to fix this SCCM Content Conversion error.

If you complete the wizard, the DP gets upgraded/reassign but the content is not (obviously).

This happens because the package assigned to this DP is not migrated to the SCCM 2012 hierarchy.

Microsoft definition of the upgrade feature :

Many customers have large Configuration Manager infrastructures and are reducing primary or secondary sites to simplify their environment. They still need to retain distribution points at branch office locations to serve content to managed clients. These distribution points often contain multiple terabytes or more of content. This content is costly in terms of time and network bandwidth to distribute to these remote servers.

This feature lets you reassign a distribution point to another primary site without redistributing the content. This action updates the site system assignment while persisting all of the content on the server. If you need to reassign multiple distribution points, first perform this action on a single distribution point. Then proceed with additional servers one at a time.

Solution :
Create a migration job targeting your packages before reassigning the DP

Bonus note: You can refer to the Hosted Migrated Package column in order to see how many packages are linked to this DP.