Low attainable rate on ADSL2+

Recently, our house ADSL2+ was having problems. We discovered the attainable line rate was very low, about 300 kbps. After disconnecting the microfilter, the attainable line rate recovered to 8000 kbps. I guess the filter is low quality, or there's something wrong with the extra cables. This is a screenshot of the normal noise margin and line attenuation, for future reference.