The camera may be set to go into sleep mode after a predetermined time. When a camera goes to sleep, whether tethered wireless or with a cable, it will lose connection with the device it is connected. The camera’s sleep parameters can be adjusted in the camera’s menu settings.
The Air Direct device may also be disconnecting because there is a “Higher” priority known Wi-Fi network available. Best practices are to set your Air Direct as the highest priority network, so when the Air Direct is turned on, your computer or phone will stay locked on that network.