Using MOV to supress voltage spikes on coils

Separate from all of that, an MOV is not the best part for this job. MOVs are relatively slow in their response to a voltage spike, allowing the spike to build to a higher voltage than it would with other devices. Also, the clamping ability of an MOV decreases with each hit. A far better part is a TranZorb. This is a specially constructed zener diode (or for AC applications, two zeners back-to-back in a single package) that can handle hundreds or thousands of amps during a brief transient - repeatedly.

ak

I havent read all of this, but something crops up in my head.
It might not be high voltage or current spikes causing this.
When thyristor/triac/ssr switching occurs there will be some ringing from the stray inductance and capacitances in the circuit, these will be in the Rf region, the semi's concerned probably wont respond well to Rf, and may not switch correctly, this goes for the ssr/thyristor device and the rectifier.
The snubber you mention, was this designed based on measured parameters or more of a empirical design?, I wonder if a more effective snubber is required.