A Drone 1900w led lightning flasher with a ssr problem. Help please
Your problem is not fly back protection which is already built-in to the SSR but rather peak current driving the 100uF input cap which has an ESR &lt;&lt;0.1 Ohm which creates a I pulse = short circuit current of LiPo’s. >200A ? 

FWIW, The pulse width must be equal to 1 picture frame or so.   

This surge current might be prevented using the SSR on the output of the booster but then the output caps may fail from RMS ripple current over time.  Adding bigger caps will make it more robust but then Voc must be tuned correctly.

So it is a sub-optimal solution due to the storage cap pulse currents in this CC,CV design in pulse mode for that DC-DC converter SSR configuration.
A better cheaper design is possible but without, use the SSR on the LEDs directly with addition cap on output such that Vout is optimized and 1 ohm series R’s are added to balance each shared LED Vf to share current equally as I have outlined in previous posts here (search my answers )