This is a common question from lots of users. However, it depends on many factors but major factor that I can figure out is that it could be due to the 2.4GHz band. In 2.4 GHz band extenders unable to provide the 100% output. I don't know the exact reason but to overcome this issue it is better to connect to a 5Ghz band. Another reason could be that your WiFi receiver is not 5Ghz compatible. Use a compatible WiFi generation product. Latest generation provide better speed and better stability. Use the latest WiFi 6 extenders. Or WiFi 6E if it is rolled out in your country. They are costly, but they are worthful.