Changed power button, front camera and earpiece no longer works
I recently got a customer phone where they wanted to change the power button on a Iphone 6 due to it not working or clicking anymore. I removed the screen, motherboard and battery without a mistake, replaced the button (after cleaning the case hole with isopropyl on a brush) and it was clicking nicely. I screwed the phone together and everything appears to work. Except when I test the front camera it freezes and the earpiece is completely silent (music speaker works fine). I try a hard reset but it's all the same. The proximity sensor works so the front camera flex isn't completely dead but it shouldn't be damaged at all since I haven't even touched it after seperating it from the motherboard. I tried cleaning the contacts but to no avail. The power button flex works too, both flashlight and button trigger.
I have yet to attempt replacing the front camera flex or the earpiece speaker as we are currently out of replacements but I'm worried it might be something else. Anyone know of a particular step with the motherboard which could affect these two things? I've been very careful with all of my screws to avoid long-screw-damage to any part of the motherboard.
Now that I think about it, something did break during reassembly. If you use the ifixit powerbutton repair guide it shows a piece attached to the top of the case, step 32. When I was screwing it back on the black plastic broke for the screw going into the back of the phone (2.6 mm screw). I didn't see any sort of connection between the plastic and the metal so I assumed it was fine. What kind of function does this part have?