Every time the nonbonded list is updated, the set of interacting atom pairs is likely to change, which can set the minimization off in a different 'direction'. It is even logically possible that a circular path could occur in this case, such that minimization would never terminate, although it is far more likely that the molecule would wander around indefinitely in a more-or-less infinitesmal space. One approach would be to set a step limit on the minimization - 100-500 is usually sufficient to prepare for running MD. Another solution (especially appropriate for fine-grain minimization for normal mode calculation) would be to set the cutoff to include the entire system and NSNB=9999999.
Bill Ross