Many things to consider:

Changed process conditions, moisture content, temperature, acid gas content, dielectrics of the dust.....

Excessive dust accumulation on the collecting electrodes (poor rapper performance) will reduce the clearances and the applied voltage. Distortion/misalignment of the H.V parts will also cause this.

Talk to the original equipment supplier. A close inspection by an expert is needed to give you the total answer.

Michael Reid. ■