Yep - I have been having similar issues with 2866ax ( see post ). I have tried various things to resolve it. Wifi disconnects regularly (e.g. once a week) and generally resolved by rebooting the router. The router also regularly and randomly reboots itself.

Our previous 2820 was pretty solid, we also have AP906 & 960C APs, but unfortunately our experience so far of the 2866ax is that it's really unreliable and not fit for purpose (we have <20 devices connected) to the point where we are considering another router brand (perhaps Ubiquiti), even with all the pain that re-configuring it all will entail. Draytek technical support are near useless too.