The attenuation is probably a rogue result, its not uncommon for modems to not report it correctly.
I'd also agree that it could be the Smart Hub 1 that was the fault. It may be the line management will remove the banding over time if it sees everything is consistently okay again, or it may need your ISP to request a DLM reset, you can never be sure. So at this point its probably just a waiting game.
Does make me think the engineer visit is possibly a bad idea right now, not sure if they will charge for it if everything is fine now. (apart from the banding)
Then again, you did say they identified an external fault, so maybe the stats improvement is a red herring and its just weather changes that has temporarily fixed it?