Use the Deployment monitor app to see the error and remove the source/ source type as soon as possible. This will lead to violation of the error for the whole license. Pool license means all the servers included on the pool not any individual. I am sure that is some bad definition/some data is there which Splunk doesn't like ;). Thanks.
No, you can see for yourself the pool would be having the license available still. Splunk does show up violation error with incompatible sourcetype/source. Kindly contact support team if you are not sure about this. But Deployment monitor app will help you resolving this error as it shows from where it's coming..