Had an annoying problem for a couple of weeks now where my gears would jump / skip but only on the lowest cog on the cassette. It's on my 1 x 10 setup and it's been driving me mad and to make matters worse, everything was new, new mech and hanger, cassette, chain, cables, shifters, the lot!! Wouldn't do it in any other gear and everything was indexed perfectly.
So my latest idea was chain line and after trying multiple positions, swapping cranks, front chainring spacing, it was still doing it and I was swearing A LOT!!
At a complete loose end I sat there, looking at it and suddenly thought 'hmmm could it be the split link?' took it apart, swapped it around the other way as it is slightly different on each side and hey presto all fine!!
I am happy that it is sorted but also annoyed that I have spent HOURS now in the garage trying to sort it and never tried that.