ASUS XT8 and RT-AXE7800 won't work together in AiMesh setup

[lucaas]

Hi everyone, I have a pair of XT8s running on firmware 3.0.0.4.388_24621 in AiMesh mode. To connect some wired devices, I bought a RT-AXE7800 (firmware 3.0.0.4.388_25058) and tried to use it as the main router and the XT8s will be nodes. The backhaul is wireless.
The router configuration for AXE7800 is no issue. After I successfully added the first XT8 as node, the uplink of XT8 is very unstable and drops out every a few seconds. And it completely disconnected after about 15 minutes. I even put them side by side and still the same.
I also tried the wired backhaul, the drop outs became to every a few minutes and after about 30 minutes it died too.
Are there any compatible issues between the ZenWIFI and RT series routers? Any idea why I can't add XT8 as node to AXE7800?
Thank you.

 

[Tech9]

This is a very strange hardware choice. Your main router has 2.4GHz + 5GHz + 6GHz bands, your nodes have 2.4GHz + split 5GHz bands. Even if this AiMesh was working properly - you can’t have dedicated wireless backhaul plus you have 6E on the main router only. What was the idea?