I've also had a lot of trouble with snapchat, I narrowed it down to times when i open the app and have a lot of unseen stories that try to load at once, I just disabled the autoloading on stories while on data and it seems to have helped a little, but it's definitely still there.
I've even been thinking of selling my 5X to get a 6P but don't know if the 6P is the same.