When new business transactions are not appearing on the Business Transaction Dashboard after deploying new code, developers should verify that there are no exclusion rules in place on the tier where the new code was deployed. Additionally, it is crucial to ensure that the Auto Discovery feature for servlets is enabled for Java agents, as this allows AppDynamics to automatically detect and name business transactions based on incoming requests to servlets. Both of these checks are necessary to ensure that new business transactions can be discovered and monitored.