This notification-carried object reports the reason a switchover occurred between two plug-in units in a redundant pair: administrative, an intentional operator-triggered switchover, pluginRemoved, the working module was physically removed, or failure, the working module failed. Admins use it in the switchover trap to immediately distinguish an expected, planned switchover from an unplanned one caused by module removal or failure, prioritizing their response accordingly. A trap carrying salixAtmfM4TrapSwitchoverReason of failure(3) tells the admin the switchover happened because the working module actually failed, warranting immediate investigation, unlike an administrative(1) switchover which was intentional.