Snapchat is throwing you out, or the app is closing?
If it's Snapchat, see if there's an update to the app. If there is, update it. If not, there's an email address on their page in the Play store. Email them.
If the app keeps closing, find it in Settings/Apps. Force Stop, then, in Data, clear the cache, clear the data and uninstall. Then run Play and install it again. (If the button says "Installed" tap it anyway. That just means that you installed the app at some time in the past.) Then Snapchat should work.