Firmware 1.1 and beyond’s new network screen shows what wifi signals the controller is seeing. Select one, then input the password to connect. If it does not see your wifi it means your controller and router/extender are too far away (must be within 10ft and clear line of site). While other devices may connect, the onefinity controller has no antenna and may still be too far away to connect.
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. 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.