Hello   @ryden 

If possible, it is recommended to test with a Wifi network for router, as mobile hotspot Wi-Fi itself could be unstable. 

• Confirm Wi-Fi network is stable on other devices, like another computer or mobile phone. 
• Try this chipset driver for Archer T3U 

Realtek Chipset Driver for Archer T2U(Nano/ Pus)/T3U(Nano/ Plus)/T4U(Plus)/T4UH/T9UH (Win7/Win10)

• Disable other network 
• For a wifi router, you could try a different Wi-Fi channel on the router/ 

If still the same, may I know what is the error when connection drops or speed gets very slow. Does this happen with2.4Ghz or 5Ghz network?

What the Internet source, it is router/ mobile wifi network?