Verify that only one Event Collector for the Harmony network is in service state. This should be the case if they share the same service group, but a missed firewall exclusion might cause two to run in parallel causing duplicated events.
IMS is the name of the obsolete and HP-UX based Advant Station 500 Information Management Station.
Today, please be more specific by using proper names like Event Storage (part of 800xA Base), Information Manager or 800xA History.
With a secondary event historian like eg IM in use, it is of high interest if duplicate events are seen in 800xA Base (Event Storage service) and/or IM.
With only one Event Collector in service state and duplicates in Event Storage, the problem is likely in the Harmony OPC AE configuration.