i think hes trying to tell you stiffer isnt always better. in fact because of it being "too stiff" its causing a binding issue, not allowing you to grab 2nd easily.
It also seems to me that he knows this will fix it from personal experience...you should probably listen to him....
its only a 20minute swap at that
edit* also when you are shifting in a turn you are putting a lot of normal force (perpendicular) to the direction of travel.
first off this is going to play a part in the ease of mechanical levers moving around such as shift linkage.
second off, why are you launching into a turn? why are you shifting in a turn? your supposed to wait until you exit the turn to shift. perhaps you should re-visit some proper riving techniques, and this issue can be avoided all together