It sounds like you have a filter running on that page that’s adding an offset parameter to your WP_Query.
There aren’t any really easy ways to search for all filters. The plugin Hikari Hooks is the simplest that I’ve seen. If you install and activate that plugin and view the problem page, you should be able to view any filters on request or pre_get_posts or other hooks that might be affecting your output. Then its just a matter of tracking down where they’re being added and disabling them before your carousel query.