Multiple errors in SMP logs related to NSE processing.
Event example:
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Unknown inventory class (AutoClassRegistration=0), entire xml node skipped: '' (c7980d43-adb3-4fc4-a97c-a35a8a195aa5, '', ''), event id=541751064, from: ffc7426e-bfbc-48c1-a912-9b03f15c0d81, to: 'Basic Inventory Capture Item' (1592b913-72f3-4c36-91d2-d4eda21d2f96), @ 2022/08/23 12:57:07 PM (age: 00:00:23) at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
at System.Environment.get_StackTrace()
at Altiris.NS.ResourceManagement.DataClassImporter.InventoryLoader.EnsureDataClassItem(DataClassSignature dc)
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Release : 8.5, 8.6
Component : Event Engine
Dataclass (guid c7980d43-adb3-4fc4-a97c-a35a8a195aa5 from above example) has been removed from the server.
Clients still have certain tasks which generate data for custom dataclass and once such NSE arrives SMP no longer knows how to process it and reports an event this dataclass information has been skipped.
Use GUID from event and search SMP database for the guid references to either find and restore missing dataclass or locate items which still reference them. Remove if necessary to stop errors.