@Q_Master 

So the Archer VR400 works as an access point and the current problem is that the speed becomes slower than before. We will do some troubleshooting to narrow it down and try to fix it. 

1. Who is your ISP and what is the bandwidth you paid? 

2. With computer connected to the VR400 by wired cable or wireless, please run the speed test and show us the results. 

3. Meanwhile, with your computer connected to the VR400, please click here to get the wired/wireless negotiation speed. 

Note: Steps are the same, while you need click ethernet connection.

4. Please connect your computer to the main router and repeat steps 2 & 3 and show us the results. 

5. Please ensure that  the firmware of VR400 is up to date. 

6. Besides, you can hard reset it and reconfigure it to give it a go. 

Good day.