that large twists grow in the magnetosphere up to a critical point beyond which no stable equilibrium solutions where found. A more detailed analysis by @Akgun2018a showed that, for sufficiently large twists, the solutions of the GSE are degenerate with several possible configurations of different energies but matching boundary conditions at the surface. This suggests the possibility of an unstable branch of the solutions and, thus, a possible explanation for the occurrence of bursts and GFs. In this work we explore this possibility by performing three-dimensional (3D) numerical simulations of the equilibrium models in @Akgun2018a. We asses their stability properties and their potential as candidates for transient magnetar phenomenology.

This work is organised as follows. In section \[sec:physics\] we review and discuss the physics involved in magnetars relevant to the processes that we want to study. In section \[sec:ff\_equations\] we briefly review the equations of force-free electrodynamics (FFE) implemented for simulations conducted on the infrastructure of the `Einstein Toolkit` (supplemented by appendix \[sec:augmented\_system\]). A detailed description of the derivation of initial models according to @Akgun2018a is given in section \[sec:twisted\_models\]. In section \[sec:simulations\] we present the numerical setup of our simulations as well as the outcome of the conducted 3D 