I am starting diving into the possibilities of planning inside Jira. After a while, I came along the function of Advanced Roadmaps. We are using the free version of Jira, but I saw the option to upgrade for free to the Premium license for a month, so I activated this. This made it possible to use the Advanced Roadmaps function.
By default there were three issue types, but I wanted to add one additional type to have a level higher than Epic. With the steps from https://support.atlassian.com/jira-software-cloud/docs/configure-custom-hierarchy-levels-in-advanced-roadmaps/ I configured the new issue type and also the hierarchy. It is now configured like this:
However, when I use this issuetypes in the timeline, I can use 'Epic' as parent of 'Dienst', but not 'Dienst' as parent of 'Epic' as I configured.

I read online that before you had a separate field for the parent, named 'Parent Link', which you had to use for a custom hierarchy configuration. Since last year, this field, together with 'Epic Link' was combined in a field called 'Parent' (https://community.atlassian.com/t5/Jira-Software-articles/Introducing-the-new-Parent-field-in-company-managed-projects/ba-p/2377758). Maybe this has something to do with it? In the parent field for the type 'Epic' I can't select a Parent, because it says that it is the highest level. But I don't understand, because that isn't the case...
Can someone help me what can be te problem here?