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.

This exact same issue with my 2927AX has been driving me insane for the past 3 months. Wifi vanishes or simply stops working multiple times a day. After trying every conceivable configuration, I went back to our old 2826AC and it has been rock solid for a week. Obviously, the speed is missing which is 99% of the reason I upgraded.

I'm guessing that no-one has gotten to the bottom of this yet but I wanted to add my frustrations to the thread.

Given that the wifi on my 2927ax appears to be very stable It's hard to know what to get to the bottom of! I have 4 x 2.4GHz SSID's and 3 x 5GHz SSID's. I only use WPA2 security on all of them as I found some time ago that various devices wouldn't connect reliably, if at all, if I used WPA3 or mix WPA2/3. No idea if that's a Draytek problem or a device problem.