Hi @Stefan Verheggen,
Thanks for your detailed explanation, I am more than willing to help you out.
According to the information you provided and the research I have done, are you opening the excel file in the local sync folder and choosing to save as a copy, but the PDF copy is saved in the Online folder? Please correct me if something is wrong.
If there is not anything wrong, it is suggested that you please manually change to a local synchronization folder when you save as a copy. The default is to save to the Online location where the file was originally located.
If you have any questions, please do not hesitate to contact me.
Moreover, if the issue can be fixed successfully, please click "Accept Answer" so that we can better archive the case and the other community members who are suffering the same issue can benefit from it.
Your kind contribution is much appreciated.