Netgear M6 Pro MR6450 vs MR6550 Very Slow Download Speeds firmware NTGX65_12.01.31.00

I have just recently purchased an MR6450 M6 Pro unlocked version in the last week. I too am having problems on the Three network in the UK with the device. Generally (apart from the odd exception, see below) really poor speeds, both in normal CGNAT mode and IP Passthrough. Tried both.

Seems to fluctuate enormously.

However at a couple of points during the last week I have got super speed from the device on Three, running exactly the same config parameters as say for instance now.

Looking at the device connection info from the admin portal, I am always connecting at "5GSUB6"  to the Three mast which is near my house. I think this is the best 5G operational mode. / frequency Three supports at the moment. At least in my area.

Here is the oddity: (Couldnt complain with this I was shell shocked when it came through. And repeated the test multple times for a few hours on that day with similar results)

My speedtest result from a few days ago : (740M download, 83M Upload) - Speedtest was performed connecting via Wifi 6E both on 5ghz and 6ghz directly to the MR6450.

https://www.speedtest.net/result/15472301035 

However as soon as I rebooted the router the next time (with the same config, nothing changed) and connecting with no real fluctuation in quality and mode to the Three 5G mast I am consistently getting speeds like this. (Still "5GSUB6")

https://www.speedtest.net/result/15483806830 

Occasionally on a few reboots on various days I might get 350M download 40 - 60M upload but this is very rare. And then on a power off and reconnect it will just drop to 20 - 40M again.

It really just seems hit or miss (more often than not miss) if I get a decent speed out of it like the 750M download test I posted further up the post. If anyone has any feedback / suggestions or if Netgear would like me to provide logs I am happy to do so.

Thanks