Interrupt for SS pin does not work properly

I am using ISR to receive commands on Arduino nano slave through SPI and reset the command at the falling edge of the SS (pin 10 is connected to pin 2) following Slave (example) using interrupt for SS pin. The problem is that the command is reset more often than I really change the value of SS pin. And I have to send the command multiple times (more than 10 times) that the slave can receive it. I would appreciate your kind feedback about what's the problem.

Does it work OK if you use the slave example which simply uses the loop() to reset the command instead of the external interrupt ?
Have got anything else in either of the 2 interrupt service routines which may cause disturbance such as a Serial.print() ?
You could try switching on the pull up resistor on pin 2:

pinMode(2, INPUT_PULLUP);

If your code is not exactly the same as in the example, then post your Master and Slave sketches here if you want to discuss it further.

he problem is that the command is reset more often than I really change the value of SS pin. And I have to send the command multiple times (more than 10 times) that the slave can receive it.

How do you know that? If you do a Serial.print() in one of the ISRs that might be the problem.

In Nicks code the command variable is not declared 'volatile', so the compiler might do weird things with it.