I'm using a spectral editor to fix sibilant vocals and it does that very transparently. Unfortunately, it's a classic case of the sibilance in the mix hitting the threshold on the original mix bus compressor (or a bad de-esser) so hard that it's punching holes on every SSS. Removing the SSS makes the pumping more audible.
I decided to try something I'd never though of before. In addition to attenuating the sibilant frequency area, I selected the frequency band below the sibilant spot and increased it by a few dB. The hole was gone AND the sibilance was controlled.
Neat Trick. Give it a try.
GR