Netgear R7000 as repeater

I have reset the router to factory defaults and tried again to configure the Repeater mode of Asuswrt-Merlin 380.65_0. However, the same issue persists: I cannot reach the parent router.

In the end I have done this configuration with Advanced Tomato 3.4 138, which does not have a Repeater mode. These are the main steps in case anyone else wants to achieve the same:

* DHCP disabled in the repeating router.

* I have set the 2.4G wireless network as an Access Point, which is the one my devices will connect to. As 2.4G has higher penetration, the 2.4G signal seems to arrive well to all the rooms.
* Channel Width for the 2.4G network: 20 MHz, to minimise collision with the neighbours.

* The 5G network, I have set as Wireless Ethernet Bridge, using the same SSID and password as the 5G network of the parent router.

* Everything else: as per default.

Now, the only downside is that the repeated network is *much* slower than the original one. With both routers side by side and my PC next to them, connecting directly to the parent router I get about 235 Mbps down / 25 Mbps up. But connecting to the repeater router I only get about 25 Mbps down / 20 Mbps up. Which is not too bad, but it is almost 10% of the speed of the original router.

I had already read that when using a repeater the throughtput would be halved, since the same radio has to be used for sending and receiving from the parent router and from clients. On the other hand, I am using an entirely separate band for connecting to the parent router (5G) and the clients (2.4G), so I was hoping this not to be an issue, or at least not to lose 90% of the banwidth.