Logback Access 2.0.1 and Jetty 11. (Probably also occurs in the previous Logback Access 1.4 series.

The issue occurs because the Jetty web server recycles org.eclipse.jetty.server.Request Objects. When the server completes processing a given Request object, the server recycles the Request Object. After the Request Object is recycled, any various data related to the previous request will no longer be available. For example, if using an appender that processes asynchronously, the Request object may be recycled before logging.

See https://github.com/qos-ch/logback-access/issues/11