Word 365 document internal hyperlinks get disrupted while saving, closing an reopening

Hi,

this issue is related to MS Word 365 running on Windows 10:

I have got one word document with document internal hyperlinks to headlines level 2 only (not to other documents or to the internet). When I save, close and reopen this document, the hyperlinks are disrupted. Before saving the links show "Active Document" while hovering. After reopening two different effects are visible:

1. While hovering the link shows the complete document path and name. These links are working.
2. While hovering the link shows the complete path and some text which is not a document name not part of the document. These links deliver error messages that the named file could not be found.

What can I do to hold the hyperlinks stable? This documents contains nearly 100 hyperlinks which I can't check and correct each time I am working with the document.

Thank you very much.

Kind regards

Frank Brose