Context: The success of software development projects relies on effective software process improvement (SPI), particularly within the agile paradigm that thrives on adaptability in dynamic markets. Objective: This study aims to investigate the barriers to effectively employing performance metrics in agile software development and to propose actionable strategies for enhancing their application. Method: Leveraging a mixed-methods approach, this research builds upon previous findings by conducting an updated literature review to identify current trends and challenges in performance metrics usage. Additionally, an in-depth case study employing focus group discussions and qualitative data analysis was performed in a real-world agile environment. Results: The findings reveal that while metrics such as story points and burn-down charts are commonly utilized, teams encounter significant obstacles including a lack of standardization, transparency, and accuracy. This paper provides a nuanced analysis of these barriers and introduces additional metrics identified from an exhaustive literature review. Contributions: This work broadens the repository of performance metrics for agile practices and offers a structured framework to address the challenges uncovered. By combining updated theoretical insights with practical recommendations, it provides researchers and practitioners with a road-map to optimize metric adoption, enabling more robust and effective agile software process improvement initiatives.