When a user-defined data list is owned or authored by a user who is not a system administrator, it takes over 1 minute to load for both system administrator and users who are not system administrators. If the list doesn't load within the 2 minutes, sometimes the error below is seen:
An unknown error occurred during the request. This could indicate a request to an invalid endpoint or a problem with the web server configuration.
We are currently evaluating this issue and will update this article when we have more information.