Yes, as explained in the FAQs, that can happen when you make certain changes to the game page.
Viewing post in My games are being deindexed
A lot of people are complaining about gettind deindexed everytime they update their game page.
You can try using butler to update your game. With butler you don't need to manually update your game page for a new update. I haven't had the chance to try this yet, since my game is currently not indexed . So I have no idea if this works.