Firewalla interfering with DHCP?

I’m in simple mode, with the upstream router handling DHCP. 

I have a number of IP range reservations based on MAC, in order to segment my kids devices, IoT, etc. 

Since installing Red, I’ve seen the IP addresses change for these devices. A reboot of the router will reset things for a while, but over a day or two, the addresses will shift, despite being set by reservation. 

The router is an older model, TP-Link Archer C7, but it’s been working fine. 

Anyone else seen this?