Draytek 2866 not connecting

Any thoughts on why 2866 cannot obtain synch to FTTC on a longish line, while older 2860 has no issue. 2866 works fine on a short FTTC line, so unit is not faulty, simply unable to connect in certain line conditions..

try a different modem code, also check the draytek forum - people have reported issues with long lines especially on g.fast units