Ballmann's higher rank rigidity conjecture for CAT(0) spaces

Let $X$ be a locally compact CAT(0) space with a geometric group action $\Gamma\curvearrowright X$. An $n$-flat is an isometrically embedded copy of Euclidean $n$-space, where $n\geq 2$. Higher rank rigidity conjecture. If every geodesic in $X$ lies in an $n$-flat, then $X$ is a Riemannian symmetric space, a Euclidean building, or non-trivially splits as a metric product. This conjecture is the CAT(0)-space analogue of higher-rank rigidity for Hadamard manifolds; the supplied source presents it as the main motivation and does not state whether it is resolved in this generality.