Facebook (De) Friend Awkwardness

So I've noticed recently that a few people that I've been Facebook friends with are no longer friends. These are people that I'm not real good friends with but actually do hang out with from time to time via mutual friends. Every time I see one of them, I feel a mutual awkwardness.

I've read stories of FB friends disappearing due to the lack of db reliability and such so I'm not sure if either party actually de-friended the other.

Anyone else encounter this weird situation or have any insight about it? I can't think of any reason why any of these people would de-friend me.