Mesh router pro not keeping DHCP reservation?

I have the bulk of my network devices set up using static DHCP reservations in the Mesh Router Pro. When trying to add a new reservation just now, however, it’s not sticking. I can add the reservation just fine, and it shows up in the “show all” list, but when I leave the app and come back in, it’s gone. I have tried both using a different IP and changing the name of the device, but every time the reservation disappears.

What might be causing this, and how can I fix it?