How to fix asus rt-ac66u router signal loss under load?

Question

ASUS

Good day, thank you in advance for all your help.
At home, an ASUS RT-AC66U router is used, with which a pyramid-shaped device called ASUS EA-N66 works as a signal repeater / amplifier.
The essence of the problem is that with any slight load on the network (watching YouTube videos, downloading any file from any site, using uTorrents, etc.), the connection to the outside world disappears and the ability to enter the router menu disappears. After reconnecting to a wifi network (from a laptop), the Internet appears, only the signal level drops from full to very low, i.e. repeater pyramid does not work. It helps to turn off and then turn on the repeater to the network, after which the signal becomes normal, but until the next use of the Internet at high speed.