Hello,

I had a similar issue with a customer and it was due to the user having a corrupted blank/empty contact in his adress book.

These entries crashes EAS contact sync on Outlook and it retries it indefinitely.

Also these entries cannot be deleted and user contact json file has to be edited manually to remove them.

It's not 100% sure the issue you have is the same but maybe can you check your user's contact to check if he has such a an entry in his contacts ? It has no name, no e-mail, all fields are empty, something looking like this:

Kind regards