RT-N66U with Merlin 374.43 having Wifi problems with second UTP-client downloading

[wasdanou]

As showing above I'm using a RT-N66U with Merlin 374.43.
I'm connected to the internet through a cable modem "Cisco EPC3928AD EuroDocsis 3.0", provider Ziggo.
So the Cisco is connected to the internet, the Asus is connected to the Cisco.
I'm using a Synology NAS to download files, which is UTP-connected to the Asus Router.
I'm also using a laptop that is connecting to the Asus over Wifi with 5Ghz.

My problem starts when the Synology is downloading, even at 100KB/s.
For the test I'm downloading a single file on the Synology, degraded the upload and download speed to half the internet speed and using a max. of 10 connections. Then I'm unable to use the internet explorer to view any site possible.
The Wifi connection isn't lost. It looks like the Asus is blocking or unable to route my browser connections.
It's definitely an asus problem, because when I make a Cisco Wifi connection during the Synology download , everything works as expected.
Also tried QoS on the Asus and tried High Priority on my laptop WiFi connection, but that didn't make a difference.

I'm still using the Asus because of the crappy Wifi speed on a previous ADSL-modem.
So I could remove the Asus and try to procede with Cisco Wifi, but it's maxed at 300Mb/s and not as the Asus on 450Mb/s.
Who can help me with this problem.

 

[wasdanou]

Some extra info

Still not found the problem.
Check some more scenario's.

Even when a download is at a 0kb/s the Wifi connection to the internet is completely shut down. Checked QoS on the Asus but this was off.
Further, with my wifi connection, going to the Asus, i'm still able to open the configuration page for the Asus router, and my UTP connected Synology, and even my Cisco Internet Router. But all http(s) traffic to the internet is blocked somehow. First thought it was blocked right up to the Asus Router, but it seems it doesn't go further then my Cisco Router. But only when I start a download from my Synology.

THis is weird. Any suggestions?

 

[wasdanou]

Fixed this problem by moving the Synology to the Cisco Internet Router, and started using the ASUS in Access Point Mode instead of Wireless Router Mode. But this raises another problem with my Cisco Router. I will start a different Forum Thread for this.