@Nargoron 

Hi, thanks for posting question here.

As you have tried many steps to fix the issue, we may need to confirm some details to understand your situation better.

1.How many clients do you have totally? How many are connected to 2.4GHz main network? How many are connected to 2.4GHz guest network? What are they separately? Did you set different wifi names?

2.When the internet is unstable, do all your clients disconnect from 2.4GHz main and guest network? Will they reconnect automatically?

3.How often does the issue happen? Does the issue happen since firmware update? When did you purchase the router?

Looking forward to your further sharing~

  @Marvin_S 

Hi Marvin,

1) how many - 3-4 devices are connected via wifi

to 2.4GHz i tried to disable all but two devices 

guest network has 2 clients most of the time

2) my experience is 2,4Ghz network drop, clients from wifi lose connection, clients in regular one signaling low signal from full because they switch to 5GHz.

Devices reconect back once wifi is restored

3) How often - we are talking about interval from 1-5 minuts

update of firmware did not help at all, same situation.

I purchase router january 2023

I hope it help,

 let me know if you have further questions

Nargoron