OK, I suggest you to analyse the other wifi signals around with inSSIDer for example... Try to force the channel width to 20MHz. My WDR4900 works great with 2.4 or 5GHz, so your problem appears very...

Hi, Try an other cable between the modem and TP-Link WAN port...

Hi, Could you give details about your wireless signal parameters ? (band, mode, channel, channel width, security, advanced setting, etc.)

The question is: what is the question?

Ask Krishna !