Running a Delta Import on the Microsoft Identity Manager Graph Connector returns stopped-extensible-extension-error .
Looking into the Application Event Log we initially see BadRequest.
Digging deeper we find DeltaLink older than 30 days is not supported.
In this particular case the Microsoft Graph Connector for Microsoft Identity Manager has not run in over 30 days and the Differential Query DeltaLink cookie that I detailed in this post and this post has expired.
The only course of action is to run a Full Import on the Graph Connector. This will result in enumerating the entire Azure AD for the Object Types specified on the configuration of the Management Agent which dependant on the size of your tenant may take some time. Afterwards make sure you run the Management Agent within 30 days (especially relevant in development environments).