Some connectors use event archives at the application. If a connector archives events, you can use the archive to troubleshoot problems with the connector. The application administrator probably needs to flush the archive periodically so that it does not grow too large.
An event archive can provide a useful backup role. If a collaboration stops running, its subscriptions are canceled. When the collaboration is inactive, the connector continues to retrieve the associated events, but finds no active subscriptions, so it archives the events. When the collaboration restarts, you can examine the event archive and move archived events back to the event notification mechanism for reprocessing.
If a connector archives events, information on administration issues is available in that connector's documentation.