Achievements not unlocking

[Cellar Door]

Specifically master of miracles and master of gestures. I've been online all the time, I've collected all miracles and gestures but the game doesn't unlock the achievements. Solutions?

[Gartz]

That's pretty weird, steam achievements unlock even in offline *(Dark Souls CAN be in offline to unlock achievements) Steam in the other hand, not. So if you play through Steam and you've flagged yourself as "Offline" or your network connection drops out, no achievement.
Otherwise I have no idea why your achievements wouldn't unlock, I had some trouble in DSIII when trying to unlock Master of Miracles and Master of Pyromancies, it only turned out that I haven't bought all the miracles and pyromancies from the npc's so be sure you have them all! Even the darn covenant rewards which are an absolute pain in the butt
Good luck!

[myoptic]

for the miracles, check very carefully against a list online and make sure you have each one on the same character. If you do, and it still hasn't unlocked, I have read some people had success discarding one of the lower level miracles and buying another copy.

I have no idea about the gestures, except to say triple check and make sure you got them all.

[Da Nut Crackah]

I actually had a similar problem getting the all miracles, pyromancies, and thus Dark Soul achievement. For whatever reason, I was online and logged into Steam, bought the last pyro and miracle I needed from Chancellor Wellager on NG+2, and nothing. Tried swapping them to item box and back, tried putting them on the ground and picking them back up (don't remember if you even CAN put them down on the ground, but I do remember trying to) and still nothing. Finally had to revert to a previous save state and buy them again from Wellager, and that time it worked. No idea what the difference if anything was, but it did the job. I imagine discarding and re-buying low lvl ones should probably work also, as Rawrk suggested.