@meryfd 

Try using these security settings for both bands:

There's a beta FW for Archer C6 which is targeted to improve wireless stability. You can give it a go. With this FW you can disable OneMesh feature if you don't use it.

You can scan for wireless interference around you and choose a less crowded 2.4GHz channel for your devices:

https://eyenetworks.no/en/locating-good-channels-bad-neighbors-wi-fi-scanner/

@meryfd 

Sorry, do you mean there is no 5G WDS bridging option on the web page? The pictures you attached seem to fail to be uploaded, please send them again.

As for the 2.4G WDS connection unstable issue, please confirm if the 2.4G connection on the C6 router is stable or not, please try terziyski's suggestion that tries to review and find a clear channel for the network first, then check again.

If the 2.4G connection on the C6 is not stable, please confirm if you are still connected to the network when the internet drops, how about the internet LEDs on the router, etc. then we will confirm what we can do to resolve it.

@meryfd 

What is the current firmware version now? Have you disabled the Onemesh on the C6 for a try? As per the screenshot, it seems that you haven't tried to disable the Onemesh yet, you can also change the wireless channels on the router after turning off Onemesh.

@meryfd 

Have you disabled the Onemesh on the C6 web GUI? As per the screenshot, it seems that you haven't tried to disable the Onemesh yet, you can also change the wireless channels on the router after turning off Onemesh.

@meryfd 

You can go to Settings > OneMesh, disable it, then confirm.