I am installing new cables and trying to reconnect the rear derailleur. I can the gears indexed perfectly on the way up but when I try to shift down from the lowest gear (biggest cog) it doesn’t move until the 2nd click. It then shift down normally until I get I get all the way down to the last click on the shifter and it skips the second highest gear to return to the highest gear (smallest cog). Anybody have any idea what is going wrong? brand new cable which has been greased well and I have checked for snags etc and all looks ok.