Nighthawk AX3000 RAK40 2.4 / 5GHz band unstable and restarting too long

Hello,

- I have a sosh fiber connection with a livebox which allows me to have good wifi speed. I've been using an ax3000 for almost 1 year.

- rak40 as an access point, it is connected to my live boxing with an ethernet cable, and the wifi of my livebox and deactivate.

- the router is placed high up in an open area in very good condition.

- I updated the router to the latest firmware version.

- my two 2.4 and 5GHz networks have different SSIDs!

- I am experienced in radio module ... and I have correctly configured the frequency bands, channels on the web interface of the router, in 5GHZ I use a channel that is not overloaded.

- all the way down the wifi configuration.

- Problem 1 that I have, and that the product is not stable, despite being able to reach the maximum speed, it often happens that in vio meting it blocks, it lags.

- Problem 2 that I have, and that I find myself forced to restart the router for one reason or another, the 5GHz network takes more than 15 minutes before being available, while the 2.4GHZ is available more quickly .

- problem 3 that I have, at random sometimes the 5GHz network disappears.

- When I see that all the radio environment that I have set up is ideal, the configuration is well done, the network coverage extends to all the rooms, I do not understand the instability of the networks, given the price of the router.

- I have a maximum speed of up to 400Mb, and I must not have cuts in video it's not logical.

I wish to have serious technical assistance, all the basic handling to do is already checked, thank you in advance.