Nighthawk x6 ex7700 drops connection to other devices

Since i connected the Extender with my Router, the wifi is bugging around. On some devices it shows no connection but it is connected to the wifi and you can use the wifi normally. Other devices aren't even seeing the wifi anymore on the list. And other devices see the wifi but can't connect to the wifi. Im using the Nighthawk x6 Ex7700 wich is connected to an Huawei Ax3 Router.