YES.

The 6dB SNR is the key to confirming that your downstream speed is "correct" at 47Mbps. There must be significant noise on te line as a 16dB attenuation can, on a good, quiet line, give 80 Mbos or greater. In your case, from what was said previously, it could be down to cross talk - one line changed over during the day, customer arrives home late evening, installs VDSL modem and suddenly the cross talk appears.

Your upstream seems to be unaffected as I would expect a 16dB line to give an attainable rate of 22 to 25 Mbps.

Can you get a tine plot from DSL Stats? Host it somewhere and provide a link - it will be worth a quick look to see.

Can I ask what you would estimate your actual line length to be? Is it around 400 to 450 metres?