I've encountered a bug with the size of your navigation bar. Not sure if this is specific to my phone/ROM or if it is for every phone, but if the navigation bar height is changed, Snapchat's image quality will decline extremely.
Above 40dp works fine (48dp is default on my phone, running a 1080p 5.2" display).
From 36dp to 40dp is where the bug occurs.
Under 36dp is fine.
Following is an album of screenshots so you can see the issue:http://imgur.com/a/ufRjP
I'm using an LG G2 D802T running Mahdi ROM 4.4.2 and Snapchat Beta 4.1.13