A VDSL2 (ITU-T G.993.2), Profile 17a, circuit has a number of bands for each direction of the data flow. Looking at the entire spectrum, from low to high frequencies, they are US0, DS1, US1, DS2, US2 & DS3 in that order. (Where US is upstream, transmit or go and DS is downstream, receive or return.)
For some reason, your modem/router has incorrectly labelled the downstream bands as DS0, DS1 & DS2 rather than the conventional DS1, DS2 & DS3. That's not a problem, though it can be source of confusion. Now I don't recognise the output . . . what make and model is it, please?
So from looking at that image, all I can say is that something has happened such that no signal is being carried in those bands which are marked "N/A". With less signal being received, the throughput speed will be reduced and there's nothing else that can be said.
I've just had a sudden thought. Are you located in the UK? If not, that would account for why I do not recognise the output from your modem/router.
Edit: I see that re0 has posted whilst I was typing the above.