I had an Archer C2300 Hardware version 2.0 where this occurred, but that router appeared to be defective for other reasons. I received and set up my replacement router (which is, unfortunately, hardware version 1.0) and it occurs with this one also.
Instead of fast page loads as when it is off, it loads the window VERY slowly, sometimes over 30 seconds between clicks. Often I get a warning that the page is unresponsive, and I am prompted to "recover the page" to proceed. This does not help.
Has anyone any ideas as to why this occurs? I have disabled IPV6 for now, but I am interested in knowing why this occurs and perhaps how to overcome it. The problem occurs with Internet Explorer11.253.113763.0, Firefox Quantum 65.0 (64-bit), and Vivaldi 2.2.1388.37 (Stable channel) (64-bit). My OS is a pretty recent install of Windows 10 Pro Version 1809 (OS Build 17763.292). My wireless network card is a Realtek 8812AE Wireless LAN 802.11ac PCI-E NIC with the latest Windows 10 drivers.
Also, it is interesting to note that the router-based speed test comes in much slower than the PC based speed test. One of the results is obviously inaccurate.