If data from external sources (e.g. SharePoint, OneDrive, Excel) suddenly isn't displayed anymore, check the following:
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First, check if the credentials (app secret, access token) haven't expired
For Microsoft, secrets expire every 12 months by default
For an explanation on how to renew these kinds of credentials, please read the article related to your external source (Configuring the Graph API (Excel, OneDrive), SharePoint News Widget)