Orion 2026.1 now features a dialog to provide a reason when unmanaging nodes:
After a little exploration, I created this SWQL for use in a widget that shows when nodes were unmanaged with the name, IP address, and reason given.
SELECT n.Caption, n.IP_Address, n.UnManaged, n.UnManageFrom, av.ArgsValue
FROM Orion.Nodes n
LEFT OUTER JOIN (SELECT a.ArgsValue, e.NetworkNode
FROM Orion.AuditingEvents e
INNER JOIN Orion.AuditingArguments a ON a.AuditEventID = e.AuditEventID
WHERE a.ArgsKey = 'Reason') as av ON n.NodeID = av.NetworkNode
WHERE n.UnManaged = 1