In three-way conflict analysis, resolving conflicts based on fewer but more critical issues can greatly improve efficiency. However, most studies on issue reduction focus on complete three-valued situation tables, while research on incomplete ones remains limited. This paper examines the issue reducts of weak alliance, weak neutrality, and weak conflict relations in incomplete three-valued situation tables using discernibility functions. First, it introduces the concept of incomplete three-valued situation tables and defines weak alliance, weak neutrality, and weak conflict relations under missing values. Then, it constructs discernibility matrices and their corresponding functions for these weak relations. The definitions of weak alliance, weak neutrality, and weak conflict reducts are provided, and all reducts are derived by analyzing the properties of discernibility functions. Finally, the proposed method is applied to NBA labor negotiations, demonstrating the effectiveness of issue reduction in incomplete three-valued situation tables.