After you set it up as Repeater mode, log into the web interface of the router, can you see USB settings in Advanced page? It should be OK even in repeater mode, but you need to set a static IP for...

Do you have a modem? Connect your PC to the modem directly and check if the modem works first. If not, contact your ISP and check the modem for you. If the modem works, can contact tplink support...

What is the model number? The model number starts with TL or Archer. So you mean there is wifi signal from the Oneplus3 device, and the tplink router connects to the wifi, am I correct? Make sure the...

What do you mean software switch? If you log into the interface of the router, go to Operation Mode/Working Mode, then you can choose 3G/4G or Standard Router. Did you try that?

Had that problem too, sent email to support.my@tp-link.com, they said they will evaluate it. You can send email too and see if they can push harder

What's the problem? Maybe can contact the local support in your country to get help.