This black screen is, in fact, a kernel panic which is caused by poor camera drivers written by Apple. As Snapchat invokes the camera as soon as you open the app, then turns it off and on multiple times, the camera drivers can crash at some point which results in a kernel panic.
The popular Snapchat tweak called "Phantom for Snapchat (Lite)" has received a new update with a new feature called "pause camera". This feature may sound pointless at first, however, it actually is very useful as it not only protects you from the kernel panics but also saves a lot of battery. Running the camera sensor in the background is very battery intense and is the main reason for Snapchat's extreme battery usage.
This update is labelled as "beta" and can be found on CokePoke's private repository.