“Breakout Room pre-assign ” menu often disappered under the "options"

Have you experience on "Breakout Room pre-assign ” menu  disappered under the "options" menu in Setting page?

I can't find  "Breakout Room pre-assign ” menu  under the "options" , sometime in Windows I can see this menu, but in Mac I can't see. and sometime it's  on the contrary.  and sometime I can's see in both platform.

Can you help to let me know the possible reason?  

thanks.