At my son's 9 month check-up, his doctor warned me that this may start to happen and is very common with babies at this age. She gave me a few reasons why babies will all of a sudden stop sleeping through the night.
The first reason being teething. Teething can be a pretty painful experience for babies and my doctor recommended giving him a pain reliever when they seem to be bothering him. I notice when he's extra cranky and moody, he'll take his toys or his hands and "jam" them into his mouth and try to bite down as hard as he can... that's when I know they're bothering him. A small dose of acetaminophen and he's good to go!
The second reason she gave me was at this age babies start to have a sort of seperation anxiety. She said that sometimes I'll notice that when I leave the room or even just put him down and walk away, he will start to cry (which he does). She said, "So, imagine being him, waking up in the middle of the night, in the dark and Mommy isn't there". Normally, he would just feel around for his paci, stick it in his mouth and soothe himself back to sleep, but since he's going through this "phase"... he wakes up and cries, instead, wanting me to come reassure him that I'm still there.
That being said, I don't think he's waking up because he's hungry or anything. I think it's just a normal phase that some babies go through. Hopefully, when the teething stops and he is more assured that each time you leave, you always come back he'll get back into his normal routine.
Hope this helps a little :D