what's the model number for your device? It seems that it can only be setup with the same day, cannot setup in different days.

What's the model number for your router? If you don't use the computer on the second floor, will you still have the problem? You can do a test, maybe it's the PC on the 2 floor take too much...

Don't use the smart connect function, it's not so smart, not better than you choose a connection by yourself.

only the speedtest is not working ? How about the internet, if you connect to the wifi or hardwared to C5400, can you browser? I recommended you to go to a speedtest website and test the speed,...

Who is your internet service provider? How about IPV4? Does it work fine?

Yes, the name should be renamed as wr(wdr)xxx(nd)_tp_recovery.bin like this format, for your model, it should be Archer VR1200vv1_tp_recovery.bin