No camera functions working

So my colleague replaced the back cover and screen for an iPhone X. By replacing the back cover i mean that we bought a new frame with the back cover already in place. After the replacement the main camera no longer works and the front camera only works sometimes.

I have tried the following:

- Replaced the main camera.

- Replaced the front camera.

- Replaced the flash and on/off button cable.

- Replaced the bluetooth antenna cable.

- Checked all the connectors on the main board and all look fine.

- Did a full reset of the phone 2 times.

All this and nothing worked. I tried turning on the flashlight as well but nothing happened. Any idea what it could be and what to try next?