Due to not much documentation i am making some assumptions here:-
wlan1 is required to carry out deauth attacks, this is why when i try to deauth a client with no second device attached to my pi zero, nothing happens and there is no visual indication that a deauth is happening.
i have tried a number of different wireless dongles supporting monitor mode and none are working in so far as i can't get wlan1mon to show as anything other than deactivated and deauth doesnt work in general.
Thanks, Matt.