Below are some reasons for the iphone camera blinking issue:-
1. There is some dirt or debris collected on the lens of your iPhone which is causing camera flickering.
2. If your iPhone's battery is low then it can have some affect's on the performance of the camera which can cause it to blink.
3. Overheating of your iPhone can also cause blinking of the camera.
If you are using an outdated version of the iOS then it can cause camera blinking.