Google Indexing Issues on several of my sites.

I have a few sites ranging in ages (one is about a year old, one is about 9 years old, and one is about 3 months old) I have seen issues in my coverage and indexing. It seems like google may be indexing some posts and then just dropping them quickly afterward. I have never had an issue before, but now I have loads of posts discovered by google but not indexed.

Has anyone had any similar issues?