If you are running Oracle Enterprise Manager (OEM) 13c, you should (must) be using Agent Gold Images (GI). They provide an easy way to manage the lifecycle of you OEM agents from a fancy dashboard.
The problem came while removing a Gold Image Versions in OEM 13.3PG. Guess what? The whole Gold Image disappeared!!!
This is not the expected behavior for this. The point here is that there were agents still subscribed to the GI. So even trying to create a new GI won’t allow us to subscribe those agents as they were still subscribed to the GI that was missing.
Using some Sherlock Holmes’ skills found that the GI was in fact still present in the OMR tables. You can use the query below to see all the GI currently living in your system.
SELECT image_name FROM MGMT$EM_GAI_ENTITIES;
What about the agents still subscribed to this GI?
SELECT * from EM_GI_AGENT_SUBSCRIBE WHERE gold_image_series='<GI Name>';
OK, so there should be something wrong here. After working with Oracle Support they found the issue and provided a patch. Please refer to Patch 28817766.
Apply this patch on top of your OEM 13.3 PG and you should see the GI again. If you are not able to see the GI, then create a new one with the same old name. Everything should look fine after that.