When a Kubernetes adapter instance is manually removed, upon restarting the Tanzu Mission Control (TMC) adapter, the deleted adapter instance doesn't get automatically recreated.
Aria Operations 8.18
The TMC adapter reads all the clusters in inventory and automatically creates a Kubernetes adapter instance (AI) for every cluster. When a Kubernetes adapter instance (AI) is manually removed from Aria Operations, the associating credential also needs to be cleaned up and removed. Since the orphaned credential existed, it prevents TMC to rediscover and recreate the adapter instance.
Clean up the orphaned adapter instance credential and restart TMC adapter collection.