The RE led is always lit? 1) Yes. Check IP address, gateway on your devices if they are still connected to the extended network. Disable and enable the wireless network connection on your devices. 2)...

How far is the HS105 away from your router? Put it in the same location as the smart switch, if the same problem occurs, it's probably HS105 is faulty. You can demonstrate to tplink support

Yes I think so.

Are you using the latest kasa app? No such problem on my app.

Yes you can use the same email account to sign in to kasa app in different cellphones. Just install the kasa app, then enter your email account and password to sign in. The smart device will display...

Check if driver update available. Otherwise, contact tplink support to figure it out.