Hello Martin,
Welcome to the Microsoft Community.
I understand that you are experiencing sync anomalies with OneDrive and are unable to restore files to the original version.
This is indeed a rare issue, but as far as I know the community has not received any feedback on such issues recently.
If you haven't made any changes and your account has not been compromised (you can visit the following link to see if there have been any recent suspicious logins), then the issue may not be related to your actions or OneDrive account, but is most likely related to OneDrive's storage service.
Check the recent sign-in activity for your Microsoft account - Microsoft Support
The Microsoft community provides technical support for users, but no community member has access to the server's back-end data to help you recover your data. It is recommended that you contact the OneDrive support team immediately for further confirmation as well as to request further investigation, as they have higher account and data management privileges.
You can send an email to the OneDrive support team by clicking the following link:
https://go.microsoft.com/fwlink/p/?LinkId=528676
PS. Before you click on the link, you need to visit onedrive.live.com with your browser and sign in with your Microsoft account, and then when you click on the link, it will automatically redirect to the OneDrive webpage to send an email.
I hope this is of some use to you.
Best regards,
Ian - MSFT | Microsoft Community Support Specialist