LM2596 random shutdown
If you're not getting hot, pin 5 might be your problem. I agree with @pgvoorhees that the layout is not ideal.  Pin 5 is directly in the current path so that at switch time it sees the current transient which can make it a different voltage from pin 3 due to the inductance of the current path.  I would try cutting the trace to pin 5 and jumpering from the diode to pin 3 and from pin 5 to pin 3 so the connection from pin 5 to pin 3 has no current.  This will keep pin 5 at the same voltage as pin 3. (too long for a comment)