Missing relations after the update from Umbraco 12 to 13

Questions
1

Hello,

after the update to Umbraco13 we are missing the relations of finite recorded documents.
In Backoffice in the new version (13), the table “Referenced by the following items” is only available for a few content items in the info. This is no longer the case for 90%, although everything is there in version 12.

The same happens in the addons we create that use the “RelationService”. The result is 98% empty.

var relations = this.services.RelationService.GetByChildId(id)

Did we miss something here? Or can someone help us?

Thanks in advance

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/113434-missing-relations-after-the-update-from-umbraco-12-to-13