Replaced digitizer and battery, now power button and camera no working

Hello,

I replaced the digitizer and battery of my iPad 3 Wifi (A1416) and none of the buttons/camera connected to the cable (see picture below) work anymore.

Opening the camera app, the camera is dark and none of the functions are selectable (e.g. switch front/back camera). It’s like the camera app is frozen. But pressing the home button works as normal.

I'm pretty sure that I didn't break any parts or cables here as I used plastic tools to unplug the cable and removed the battery from the other side (left side in the picture above). Moreover, I was also very careful when scraping off the broken screen in this area.

Now, what's not working is:

- Power button (lock button) doesn't do anything, even on long hold

- Opening the camera, the screen is black and I can't revert to back and front

- Neither volume, not mute buttons work

- I can't lock the screen, even with the assistive touch "Lock screen" button. This, however, has I "solved" (more like a temporary fix) by disabling in Settings > General > Lock/Unlock. (Some issue apparently with software or magnets)

I tried to reconnect the cable multiple times, to make sure it is stuck in correctly - but nothing changed.

Anyone has any idea what is wrong here or how this could be solved? Thanks a lot for your time taken reading :)

p.s. Here are some additional pictures below