I think we need to see the
full stats, preferably both before and after for comparisons sake otherwise it's going to be pure assumption on what has actually changed. If there is confusion to where those stats are, just post here and someone will be able to help.
I can see you are using DSLstats so presumably you have data logged and graphed?
I can see the SNRM has dropped to ~6 dB from ~19 dB on the upstream which would means there is a lower overhead for noise. The graph you have provided shows
FECs, which have increased on the upstream and remain mostly the same for the downstream. Though FECs are usually no big concern and it would imply that your line has interleaving on but the drop of SNRM will certainly increase the FEC count.
My assumption is that perhaps your upstream has been uncapped (from 448 Kbps). This may have been because of an upgrade to ADSL2/2+ capable hardware at the exchange, especially since you have said telnet says ADSL2 modulation mode.