Ignore the 20Mb IP profile.
That's obviously incorrect as you are getting higher than that on speed tests.
The TBB test seem to be more accurate than the BTw tests.
37/8 is about right for your sync speeds. 37/17 is impossible.
The drop in speed over time is expected. It's called crosstalk and is the effect of other lines on the cabinet emitting interference/noise.
Those who took FTTC early are likely to notice this much more as they subscribed with little noise and got high syncs.
Then as the cabinet fills their sync is reduced by crosstalk.
For your attenuation your sync isn't out of the ordinary.
In short, the BT Wholesale speed test is garbage, broken, unreliable.
The browser used can have a huge impact on the speed it shows.
Edited by j0hn83 (Tue 08-Oct-19 14:01:12)