Offline devices can be found on the DHCP tab of all places: Advanced Settings / LAN / DHCP Server: Then click in the box to select a MAC address to add as a static IP and there's a link right down at the bottom right that says "Show Offline Client List"
It truly could not be more hidden imho!
Ah yes I've discovered this 'undocumented feature' of this version too! Does seem to be rectified by a power cycle, but really shouldn't have to resort to this.
HomePod mini connection stability and general Apple Home response has been awful in my two node setup on this release. Rolled back to ASUS ZenWiFi BQ16 Firmware version 3.0.0.6.102_37012 and stability returned.
Hence why I started my comment with 'Not quite sure…' so your reply is terse to say the least. What a pleasant entry to these forums for me. Oh and with BQ16 would that not be Quad-band?
Not quite sure if there is technically a problem with doing a factory-default reset and then importing a saved settings file? Seems to have worked fine on my BQ16 pair doing this. Other than as has been mentioned the SSL/TLS cert not playing nicely with Safari - but then that's nothing new for...