This is my second Archer C7 - had a v1 for a few years and recently upgraded to a V5.  I did not notice this issue on V1 as we only made use of the 5GHZ band.  I went with the V5 as we are also using the mesh configuration with two extenders.

Anyways, long story short..

- No matter what device (laptop, tablet, phone) the speed is either very slow or very fast and it can constantly change from one to the other on a minute by minute basis.

- Simple things like fb comments or a full website will sometimes not load while connected to the 2.4 band with good signal strength.

- Sometimes the google speed test can turn out 18-20+ mb/sec and other times it does not even reach 1mb/sec.

- Reeboots, router re-configurations/etc ... all no change.

- Wifi channel is clear (as per scanning app)

- Desktop PC is wired to internet modem and it works amazingly fast .. connect is a 1gb with Rogers (Toronto)

- Having the extenders connected/disconnected does not change the situation.

- The 2.4Ghz band is set to 802.11n only.

I have followed the troubleshooting guide for "slow wifi" and we are now at the end with no change to the performance.

As an example, when I have the wifi settings open on one laptop (not doing any activity, I can see the connection type/speed going anywhere from 30mb to 140mb to 300mb .. and the performance is still terrible. During the tests below the laptop is the first device and network connectivity said it was a 300mb connection, then 160, then 120 and then currently its now back upto 300 after saying it was 270 for a few minutes.

As an example of speed tests (on 2 different devices) that were both done back and forth on the devices.

1.27Mb/sec down - 7.83Mb/sec up

5.37Mb/sec down - 3.81Mb/sec up

3.46Mb/sec down - 7.38Mb/sec up

4.34Mb/sec down - 6.09Mb/sec up

1.94Mb/sec down - 1.27Mb/sec up

17.8Mb/sec down - 30Mb/sec up

18.7Mb/sec down - 25Mb/sec up

17.5Mb/sec down - 19Mb/sec up

8.5Mb/sec down - 23Mb/sec up

The 5Ghz band is currently reserved just for streaming video devices in the house and it has had no issue.  When, as a test, I add any of these devices to that band the speed goes up dramatically and performance remains stable.

I dont know what else to do or try and I dont want to, or feel I should need to, put everything onto the 5Ghz band when most of the devices are just doing basic browsing with the odd video stream on youtube/zoom app/etc.

Any assistance is much appreciated.