Resolution of the Gribov copy problem
Establish a complete and rigorous resolution of the Gribov copy problem in Landau-gauge Yang–Mills theory, determining how to consistently treat gauge copies in the functional integral beyond the Faddeev–Popov action so that infrared properties can be derived from first principles.
References
Of course, finding what this something else is is a complicated matter because it relates to the Gribov copy problem which remains an open problem to date.
                — Aspects of confinement within non-Abelian gauge theories
                
                (2404.06118 - Reinosa, 9 Apr 2024) in Chapter “Thermal Gluon Average”, Section “Infrared Gauge Fixing”, Subsection “Lattice Results”