Which setting causes the system to check for conflicting updates in a custom record instance?

The setting that causes the system to check for conflicting updates in a custom record instance is "Enable Optimistic Locking." This feature is designed to prevent issues that can arise when multiple users attempt to update the same record simultaneously.

When optimistic locking is enabled, the system maintains a version number or a timestamp for each record. When a user tries to save changes to a record, the system checks whether the record's current version matches the version the user retrieved when they started editing. If the versions do not match, it indicates that another user has made changes to the record since the first user retrieved it. Consequently, the system prevents the update and can prompt the user to either discard their changes or merge them with the most recent version.

This setting is particularly important in collaborative environments where multiple users might access and modify the same data concurrently, ensuring data integrity and consistency in the system. Other settings, like enabling inline editing, enabling system notes, or allowing child record editing, serve different functions within the NetSuite environment but do not specifically address the issue of conflicting updates.