Why is my fan circuit with SSRs short circuiting on power down?
I notice your hand-written notes on the schematic.

Figure 1. Details from the schematic.
I suspect that on switch-off that you might be getting a high \$ \frac {dV}{dt} \$ (very sudden rise in voltage). Triacs can be turned on when the voltage across their MT1 and MT2 terminals rise suddenly. It may be that this is turning on A and B simultaneously and shorting the motor windings as indicated in your note. This in turn may cause high current to flow and destroy your triacs. You'll need the appropriate snubber for this.
Links

Phase Control Using Thyristors by Littlefuse.

Thyristor Theory and Design Considerations Handbook
 by ON Semiconductor.