Thanks for the reply, Dem0ns.
To clarify, are you only using the camera to take a photo first, or are you able to use the QR reader when selecting the code scanner in your Control Center?
Just in case, try adding the code scanner to your Control Center using the steps below, then test if that helps:
1. Go to Settings
> Control Center.
2. To add or remove controls, tap
or
next to a control.
3. To rearrange controls, touch
next to a control, then drag it to a new position.
You can then select it from your Control Center using the additional steps here: Use and customize Control Center on iPhone - Apple Support
All the best.