Cannot decode raw data (NSURLErrorDomain:-1.015

I have this strange error.

For all users, the mail application works fine, but I have one user who, when accessing the app, gets the error ‘cannot decode raw data (NSURLErrorDomain:-1.015)’. The strangest thing is that this only happens when I use the link in the top bar. If I click on any email in the dashboard, I don’t get this error.

I have no idea how to fix or verify what is happening. Can you help me?