Do you have a computer which can be connected to LAN port of WA730RE? Is it Windows or MAC? There is an installation guide for MAC computer. If yours is Windows, follow the second instruction and...

Did you get it resloved? Or did you try the old firmware? Anyway, you can submit a ticket but not sure if TP-LINK people can reproduce the problem in their lab....

Maybe the guide below will be helpful. http://www.tp-link.com/en/faq-512.html

During rebooting process, the extender will turn off, back on and boot up. It is normal that you cannot browse the page. Any problems with your internet connection?

I didn't figure out which one is working as the main powerline adapter that connected to the router.

Did you check “Use default gateway on remote network”? If IP Address pool is in the same range of LAN IP address, it should be Okay. But if IP Address pool is in different range from LAN IP address...