Drop outs and occasional very slow (unusable) speed...

[#1]

That is exactly what I was looking for, you were correct to obscure you username. 

Your Hub One has an old firmware version it should be 4.7.5.1.83.8.289.1.3 not sure if it's relevant to your issue but it's always best to have the latest. 

Any reason why you have not disable the Hub's wireless?

Using a wired device I would suggest running https://speedtest.btwholesale.com/ this tests the speed of your line and will report back your IP profile if you run the Additional Diagnostics, although the sync speed looks good on the Hub your IP profile might be banded to a slower rate for what ever reason the DLM decides it's best to be. You line attenuation suggests your not far from the green cab on your road.

Edit @TheMightyAJ the Hub One firmware is out of date, is that something you can arrange to be corrected?

[#2]

@Dan_the_Van 

There are inferences in here that the WiFi set up is complex ... and the Hub One has been left to channel flip.  Given that WiFi appears to being used as the back haul, is it feasible that frequent channel hopping might give rise to the reported experiences?

Is there merit in fixing the WiFi channels?

One hopes that the devices are only using channels 1, 6 or 11 ... and no one nearby is using any other!

[#3]

@Townman 

the Hub One has been left to channel flip

Given that WiFi appears to being used as the back haul

My reading of the thread I see 

Post 23 - Yes, I have a BT Whole Home Mesh Wifi 3 disc set. All wireless devices connect to this. The primary disc is wired to the router via ethernet.

The attached log file on post #10 shows no connections to ath00 or ath01

Later on the OP said 

Post 26 - In regards to the BT Discs. All have strong signal on all BT discs according to the front lights (they are wired).

[#4]

@Suarez 

just a thought, I would suggest turning off the Hub One wireless, not that you are using it.

Regarding the BT mesh, are they ALL set to use the same channel. The reasoning behind using 1,6 or 11 is the channels do not overlap the transmission frequencies and the device will attach to the strongest signal with out the need to switch channels

Dan.

[#5]

Regarding the firmware, the version is new enough that carrying out a factory reset should update you to the latest version within the next few days, as far as I can tell. That being said, it looks like a new router's been ordered today anyway, so it might be worth waiting until that arrives and then comparing and contrasting the performance from there onwards.