The magnets haven't been trained up to their full power yet, so my understanding is they are expected to be a bit unstable. The "training" process sounds like it anneals defects out of the superconductor material, involving repeatedly deliberately raising the field to the point where quenching occurs, then re-cooling of the magnets and starting over, to allow them to reach higher field strengths. I would expect un-trained magnets to be more sensitive to stray particles and other quench causes as well.