I guess you are simulating a metal material? if so, I would suggest to use PEC to replace it, if it is ok.
Please note again that, to get proper simulaiton accuracy, mesh accuracy 2, 10 mesh cells per min wavelength inside the max refractive index (pure dielectric. otherwise you will need to resolve the skin depth) is recommended. you may try mesh accuracy 1, which is 6 mesh cells per min wavelength. Smaller than this is not recommended. If you artificially make the mesh larger using override mesh or other method than the requited mesh density, the simulation accuracy is not guranteed.