I think you missed what I was trying to say. No problem!
So iPhone shipped with an app named "Camera", this is native to iOS. Which means you didn't have to download it from the Appstore (aka 3rd party developer)
Many apps like Snapchat, and Instagram have the software to trigger/use the camera on your iPhone. However if the software is malfunctioning, or not working correctly at the time it may cause issues loading ect,..
Therefor I ask you to use the native camera App, and see if you have the same shaky experience with that.
Kind regards,
K