Wifi at 5GHz is unstable at 18.06.1 . I built from source yesterday a new firmware and nothing changed. The picture i attached shows the problem. Every couple of minutes the connection drops. I tested with 3 devices and they reproduce the same behavior therefore the router is the causing of the problem. This behavior was present 6 months ago when i first build and install the lede firmware. I hoped over the time to improve. I guess we should inform the developer of the wifi driver. Reporting here seems the like wrong place for things to be fixed.
Edit: I must also mention the test conditions: The router is 3 meters (10ft) away from the receiver. There is no other station at 5GHz and im nowhere near any airport. I used iperf3. Sending from the router to the device there is a faster connection around 200Mbs yet there is a lot of drop packages every couple of minutes. Sending from the device to the router the connection is more stable with only maybe 30 to 50 packages lost every couple of minutes. Yet the later is slower for some reason around 130 to 150Mbs.