Two chime 2nd generation keep going offline

Just bought two chime 2nd generation chimes a couple of weeks ago. I tried to connect them to my Chime Pro (1st generation) and also tried to connect them directly to my wifi router. They can connect for a while (maybe 10 mins) and then goes offline. Each chime's signal was below RSSI -40 (Green color which means good signal strength I think ) and each chime shows solid blue circle light. I tried to reconnect to the wifi and/or reconnect to chime pro. The same thing happened: after new mins, both devices were reported offline in the ring app. Does anyone have the same issue? Is there any way to fix it?