I have created a lookup for a threat feed CSV file we are using.
After deleting all the Lookup CSV files and removing all the peops.conf and Transforms.conf inputs for this lookup from the the deployer, CMn SHs and indexers I still see an error
The first thing to check would be the method used to remove the artifacts. Did you remove and modify from the file system or did you use Splunk Web to do so? If former, you'll also need to restart Splunk server.