Legend Achievement now only for solo players!?!

Earlier today, my progress for this achievement was 32 / 40, then all my locked achievements got reset, and now my progress is 19 / 40, which are the missions I completed by MYSELF! The legend achievement DOESN’T say solo or co-op, so I’m VERY frustrated about this; I did 13 MISSIONS with my friends, and now its for NOTHING!! Is anyone else having achievement problems; if so, RAGE on similar fourms to get 343’s attention on this problem!!! >:(

relax man. its an easy cheevo. just play solo. if your having trouble with it just play 1 or 2 missions a day