Same for me - hitting "C" like the popup states just throws me out of the race with no further explanation.
Annoying, very. 😞 Especially as it seems to be a resurfacing bug.
Filed a bug report ingame - I hope this gets fixed really fast as it literally stops me playing the areas in Path of Fire (otherwise I'd waste EXP as I don't have any Mastery left to develop until I finish this achievement)