Conduct a thorough investigation into the various issues affecting the functionality of the application. Specifically, focus on the non-operational functions that are failing to execute as intended. Additionally, assess the responsive design of the user interface, identifying any elements that do not adapt properly across different screen sizes. Provide a comprehensive overview of the current setup, including any relevant configurations or code structures that may be contributing to these problems. Suggest targeted improvements to ensure that all functions operate correctly and that the UI is fully responsive, enhancing the overall user experience.