My iPhone 6's camera is malfunctioning?

I recently got my iPhone 6 fixed for a broken LCD. Everything's working well except for the camera.

1. Whenever I open it and it's on the 'photos,' 'square,' or 'panorama,' it only shows a black screen. I need to switch to 'slo-mo' and 'videos' where the image shows, then back to photos, for it to work.

2. When I use the front camera, it won't switch back to the rear, and vise versa, when I'm on these tabs.

3. It takes videos, but not photos. When I press the capture button, it only blinks but it really doesn't save. So I have no idea if it took the photo at all. It only takes a photo when I use the flash or burst. Or when I use messenger, snapchat, and instagram.

Any idea how I can fix this? Thanks in advance.

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