Umbraco 13 RTE Issue in the backoffice

We upgraded our website from Umbraco 12 to 13 and now we having this issue in the backoffice where the content of RTE is not showing. It only shows [object Object]


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/113960-umbraco-13-rte-issue-in-the-backoffice