Model : TL-WR740N / TL-WR741ND

Firmware Version: 3.16.9 Build 150605 Rel.41251n
Hardware Version: WR740N/WR741ND v5 00000000

ISP :Skylark ( my local isp)

Hello all,
My ISP provide separate bandwidth, for other websites 512kbps :( and 10 Mbps :) YOUTUBE bandwidth.
So my legal speed is 512kbps :( and only for YouTube bandwidth 10 mbps :)

Now problem is that if i connect my ISP connection direct to my laptop or desktop everything works fine :) my legal bandwidth isn't affected by YouTube videos and at YouTube no
Buffering i can watch in HD no problem at all, but when i connect through my TP LINK router TL-WR740N / TL-WR741ND my legal bandwidth is being affected by YouTube videos
and first time when i watch a video it starts with 144p :(:(:(:(:( if i manually set it to 720 or 1080 it start buffering. Then trying everything i discovered
that if i reload the same video page
twice or thrice video play smoothly in HD and my legal bandwidth isn't affected by YouTube so why my router is causing this problem.

Little about my connection details

My ISP give connection through Mikrotik
My setting is Static IP
IGMP Proxy is on

My settings









Please anyone solve this problem.