Personal opinion: as there are many factors may affect the internet connections, and every user has differnet network environment, so it's suggested to email TP-LINK support to get assistance as per...

Please check your router DHCP Settings, or you can contact tplink support for remote control analysis.

New UI, cloud feature

The system is Win10 1709,right? you can try to join Windows Insider Program and upgrade to 17025

I think this may be helpful. http://www.tp-link.com/en/faq-900.html Some email like Gmail you should login account and modify the security first.

Check if your phone still connects to the Tplink smart home network when it shows not able to connect. It may disconnect since there is no internet and connect back to your home network...