After many months of steady service of my static WAN IP my supposedly static WAN IP address changed and many of my device therefore stopped working. Why did this happen? I thought I registered for a static address?

Have you updated your IP on the system ?

Dynamic DNS service does not provide you with a static IP address but maps a static hostname such as yourhome.dynu.com to dynamically changing IP address. An IP update client needs to run within the network to keep the IP current.

Can you please clarify which "system" you are referring to.

Thank you.