Within linear continuum theory, no magnetic texture can propagate faster than the maximum group velocity of the spin waves. Here, by atomistic spin dynamics simulations and supported by analytical theory, we report that a strongly non-linear transient regime due to the appearance of additional magnetic textures results in the breaking of the Lorentz translational invariance. This dynamical regime is akin to domain wall Walker-breakdown in ferromagnets and involves the nucleation of an antiferromagnetic domain wall pair. While one of the nucleated domain walls is accelerated beyond the magnonic limit, the remaining pair remains static. Under large spin-orbit fields, a cascade of multiple generation and recombination of domain walls are obtained. This result may clarify recent experiments on current pulse induced shattering of large domain structures into small fragmented domains and the subsequent slow recreation of large-scale domains. Antiferromagnetic systems are becoming an appealing alternative for spintronic-based devices due to the more rapid magnetisation dynamics when compared to their ferromagnetic counterparts. Here, using spin dynamic simulations, the authors demonstrate that the motion of domain walls can achieve supermagnonic speeds in an antiferromagnetic system by means of generation of additional domain wall pairs.