Sanity-check on snubber design
I suggest you read TI app note SLUP100, "Snubber Design" by Philip C. Todd for some good background on snubber design.

When the triac is on, the dissipation through the snubbers will be low since they are 'shorted' by the triac.

When the triac is off, load current is going to try and flow through both of your snubber circuits, and the resistors are going to see power dissipation.

Are you absolutely sure that the triac is firing each cycle?