Contacts vanishing from my Nexus and Gmail

[AC Question]

My contacts are vanishing. There is no particular pattern. I have 2000+ contacts in my Nexus 4, all stored with my gmail account. Sometimes, I add a new contact, it's saved, shows up for a few days and then stops showing up. Sometimes, I find a very old contact that I entered few years back has vanished. I am pretty anxious. Any reason?