Move the node/2nd router closer to main router. If possible there less wall in between both router for optimal connection. It will be better if the connection is wired instead of wifi so can easily get full speed. Sometimes even changing the side of same wall can do wonders on the wifi coverage. Just notice it this week on setting up office wifi. From a deadzone even at 2.4Ghz to ok now the whole 3 storey building have wifi. Be ready to be a handyman & chargeman lor.
Good thing about Asus Aimesh can play around with node for optimal wifi coverage before drilling a hole.