The configuration for Slide Update with counterparts must be disallowed.

This setting controls whether users can link slides in a presentation with their counterparts in a PowerPoint Slide Library. If this policy setting is enabled, PowerPoint cannot check the status of a slide in a Slide Library when a presentation with Slide Update data is opened. If this policy setting is disabled or not configured, each time users open a presentation that contains a shared slide, PowerPoint notifies them if the slide has been updated and provides them with the opportunity to ignore the update, append a new slide to the outdated slide, or replace the outdated slide with the updated one.