  Regular black holes with nonsingular cores have been considered in several
approaches to quantum gravity, and as agnostic frameworks to address the
singularity problem and Hawking's information paradox. While in a recent work
we argued that the inner core is destabilized by linear perturbations, opposite
claims were raised that regular black holes have in fact stable cores. To
reconcile these arguments, we discuss a generalization of the geometrical
framework, originally applied to Reissner--Nordtsr\"om black holes by Ori, and
show that regular black holes have an exponentially growing Misner--Sharp mass
at the inner horizon. This result can be taken as an indication that stable
nonsingular black hole spacetimes are not the definitive endpoint of a quantum
gravity regularization mechanism, and that nonperturbative backreaction effects
must be taken into account in order to provide a consistent description of the
quantum-gravitational endpoint of gravitational stellar collapse.
