The Data Aggregator Item was deleted using its ItemID and a call to DA:8581/rest/devices.
After this an error was seen in the Performance Center logs regarding "PRODUCT_ID_CHANGED" for the Data Aggregator Data Source.
With that resolved we now see the Data Collectors missing it's Devices and Polled Items.
This was done in an attempt to resolve a problem where some managed devices were showing a lack of response to poll requests.
The deleted Data Aggregator Item results in a disconnect between the Data Collectors and their managed devices.
All supported DX NetOps Performance Management releases
!!!!NEVER DELETE THE DATA AGGREGATOR DATA SOURCE OR IT'S ITEM WITHOUT DIRECTION FROM SUPPORT AND/OR ENGINEERING!!!!
The solution involved a complex series of queries to determine old vs new ItemIDs.
We then utilize those values to update the Data Repository Database to fix the broken relationships between the managed devices, the Data Collector polling/managing them, and the Data Aggregator.
Please engage Support with a new Support Case for assistance in resolving this problem. When doing so please reference this Knowledge Base article.