When this occurs, prior to the release and renew... from the STATUS tab >> DEVICE INFO page note the DNS Address(s). Next, perform the release and Renew. Do you still have the same DNS Address(s) that were noted? If they have changed, then, you need to discuss with your ISP why this is occurring. Usually even if your DNS Address changes it should not stop request from reach the specified DNS Server. Let us known what you find?