Hello @Smits David ,
Welcome to the Microsoft Q&A platform, and thanks for posting your query.
We apologize for the inconvenience you have encountered.
I have noticed that a similar issue has been discussed here. Could you please check and see if this helps.
Here are the two potential issues discussed on this thread.
- Could be an issue with Permissions
- another reason could be with Disablecustomappauthentication
In case, If this resolution didn't help, I would suggest opening a support case for a deeper investigation. If you don't have a support plan, please let me know. I can provide you one-time free support request.
I am looking forward to hearing from you.