When I installed it in it's permanent location, it is connect through a AT&T gateway which requires that the code request an IP using DHCP rather than pushing one with a IP declared in the code. At my house, I did not use DHCP.
The D stands for dynamic. Dynamically assigned IP addresses are not permanent. They expire after some period of time. Once the IP address expires, it is no longer valid, and can no longer be used.
You'll need for your Arduino to be aware of that, and to request a new IP address before, or just after, the current one expires.