Band Plan "confusion"

I am wondering if it is possible for an incorrect or corrupted band plan to be loaded and run on an FTTC modem.

I have an 80/20 service and until yesterday received 56-58 / 18-19 and perfectly happy and it has only dropped 1-2 Mbps on the downstream since install - the line is actually 600m long.

Needed to reboot the modem yesterday and am seeing a problem I last had 18 months back. My UPstream has dropped to 9.2Mbps which I noticed when trying to do some major work uploads.

Have now run the TBB speed tests and the results there are 68 down & 9.2 UP. Te BT Wholesale gives 70.47 actual with 70.66 max down and 9.07 actual with 20 max achievable on the upstream..

So, where has the extra 12Mbps downstream come from? And where has the upstream gone. It is rather suspicious especially as my upstream have an SNR of about 12dB indicating that there was spare capacity over the 20Mbps.

I wonder if an incorrect Band Plan has bee implemented reducing the number of UPstream down and increasing the down stream?

Band plan as in one of the 3 ANFP power masks or referring to a misconfiguration of the line card to limit upload to 10 Mbps

To get to the bottom of either, then bits per bin plots really needed from before and after

Probably the former ... The UK uses 998 and there are other alternates in use elsewhere. That is the basic question as 10Mbps lost from UP and 12Mbps gained on down.

Cannot get plots at present as I only has an ECI modem - need to get my Huawei back to access the stats.