Sorry I don't know any method in alternative firmware. Please direct your question here: https://forum.openwrt.org

The cable that connects modem and routers is original or not? What kind of WAN settings do you have (Dynamic, Static, PPPoE etc)? This update was properly executed? Do you have access to router...

No problem, greetings from Poland!

You have to send those informations here. May be it's some bug in firmware - http://ticket.tp-link.com/index.php?/Core/Default/Index - I can hear about it first time.

[QUOTE, you'd better contact the shop for replacement under warranty. ][/QUOTE] Problem with the power supply, go back router to the shop if you have warranty

Give us screenshot from status of your TP-link, we like to know something about your WAN.