Port Forwarding no longer points to correct IP

For about a year port forwarding was pointing to the right IP address. Nothing has changed except for the IP address assigned to the device, via DHCP, from the router. App still sees the old IP address, not the new one, no matter how many times I remove and readd it. I've tried reserving the new IP address to the device on the gateway itself, I've tried doing a trick I saw on a 4+ year old thread (clicking DHCP and save, despite it already being DHCP, on the gateway then /release /renew). I don't know what else to do.

The MAC address is correct, the device name is correct, the IP address is being pulled from some stale cache that I can't refresh with anything I do.