  We study the effective potentials for various probe branes surrounding
AdS$_4$ black holes with massive halos in consistent truncations of M-theory on
the Sasaki-Einstein$_7$ manifolds $Q^{111}$ and $M^{111}$. These probes are
either M2 branes extended in spacetime or "particle-like" probes such as
internally wrapped M2 branes and, upon reduction to type IIA string theory, D6
branes corresponding to baryon operators in the dual Chern-Simons theory. We
find both global and local minima of the potential outside the horizon,
indicating the existence of stable and metastable multicenter AdS black holes
in the extreme mass ratio regime, at fixed temperature and charges. For the
planar case, we also find an instability towards nucleation of
spacetime-filling M2 branes. With this analysis, we address some open questions
on the holographic description of glassy phases of matter.
