If it's really necessary (and I know it is, I'm in the same boat as you and have been complaining for a while about the limited number of DHCP reservations available) you can set some of your clients to static addresses on their end, saving your reserved DHCP static lease slots for those precious little snowflake devices that don't allow client side static IP configuration.
Easily done if you are technically inclined. I am not, so it was miserable, long, and not at all fun. Oh...they also don't show up in the WebUI. That list only shows devices whose IPs are handled through DHCP. If you want know if they are connected, the mobile app will eventually list them when it gets around to it. So if you were hoping for a global list of all connected devices independent of HOW they get their IPs somewhere in the WebUI, that would be a firm no.
But I'm not bitter.