Kathy_Z  

I want to answer your question step by step;

1. Router is Huawei HG255S, it was came from Turkcell in Turkey  for fiber. Im sure that it is stable router because different devices have not a problem like that. So they are iphone 8 plus, iphone XR, macbook pro, hp elitebook. 

2. Connection lost on desktop not from router. When connection is lost on desktop, I saw that my mobilephone has a connection and I browsing. 

3. Approximately 5-6 meters then there is no obstacle.

4. I dont know how to change bant channel :( 

5. Last version is 2019 then I have reinstalled many times.

6. I bought 2-3 month ago on amazon.com.tr

Thank you for your attention :)