Hi @Urs van Wintkers ,
I suggest you refer to this similar thread, I found this behavior is related to update for Office: https://techcommunity.microsoft.com/t5/office-365/table-of-contents-links-not-working-when-save-as-pdf/m-p/2839238
In my opinion, you can give a feedback to Microsoft about this problem:
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And as a workaround, you can try to roll back to the version without this problem, for example: 16.0.14326.20404
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