Copilot Studio agents problems connecting to Sharepoint knowledge source

I would start with one affected agent and one known SharePoint page that used to answer correctly. Re-index or refresh that knowledge source, then ask the agent a question whose answer appears verbatim on the page. In parallel, test whether the same user can find that content through Microsoft Search and open the file or page directly. If direct access and Microsoft Search work but the agent still answers as if the content is missing, collect the agent ID, SharePoint site URL, failed prompt, timestamp, and environment region for a Microsoft support case. That evidence points to retrieval rather than permissions.