Most likely a weak wifi connection to the controller.
- If the controller connects one day and does not connect the next, it’s typically one of two things. First, the extender/router is too far away and the signal is going in and out (must be within 10ft and clear line of site). Move them closer together. Second, your router/extender is setting up a dynamic IP address (that changes every so often according to the routers needs, could be hours, days, weeks) and the IP address is changing. Look into setting up a static IP address (this is done with your router/extender, not the controller). More info HERE.