AC68U - Network slows to a crawl when a device is downloading

[80A0F4E3F8C61]

It seems like whenever a device starts downloading using a Chinese download programmed called "Xunlei" it slows down the entire network to a crawl even if its not using 100% of the bandwidth.

e.g. Download speed is 150mbps, set QOS to limit that specific device to 50mbps. It does limit it to 50mbps but it still slows down the entire network to a crawl. Even google.com takes forever to load.

Whats causing it to slow down the entire network while not even using 100% of the available bandwidth? Is there a way of limiting that downloader?

Thanks.