"Complex issues" refers to problems or subjects that are difficult to understand, analyze, or solve. These are situations that involve various factors, multiple perspectives, and are not easily resolved. Full definition
I have been involved in a number of reported procurement litigation cases dealing with complex issues of procurement law and judicial review. (bevanbrittan.com)
Overview Climate change is one of the most complex issues facing policy - makers today. (cfr.org)
Cases are fact specific, typically with complex issues of proof and fault in dispute. (psp-law.net)