Since repairing the screen, I have noticed that the battery temperature sometimes registers as -30.0 deg C. This causes...

Did you check the battery temperature? I currently have an issue (and as yet unanswered question) that really charges slowly if at all when the temp marks as being -30 degrees C. Apparently, the phone won't charge the battery at certain temperatures

Yes. After getting my screen replaced the screen immediately turns off when placing a call (or answering) without letting you turn it back on, until the call ends.. sounds like your issue? The problem is with the proximity sensor always detecting something "near". you can confirm this by accessing the service menu (pls google it) or using an app to monitor sensors from the play store. Since I had to get my screen changed professionally (I previously failed to change the screen - it wouldn't stick to the chassis correctly) I'm hesitant to open the phone up again out of fear that I'd end up screwing something up again. I suspect that the proximity sensor must be misaligned in some way and is picking up the case itself in it's visible range. as a work around, I disabled the proximity sensor by installing Xposed installer from the play store, then installing the "disable proximity sensor" module from within it. I'm assuming you'd need a rooted phone to get this to work. This will however not turn off the...

A grey white washed screen? I experienced this problem when replacing my screen and found out why this is happening.. When connecting the ribbon from the screen onto the bottom board that has the charging port (this), the ribbon has a small amount of circuitry and components (the second piece from the left). The original would have adhesive to stick to the (charging port) board, and the absence of that means that the circuitry will touch against the metal part of the (white) antenna cable that is connected there too. After trying (and failing( to adhere the ribbon firmly to the board underneath, I simply cut a small piece of electrical tape and placed it in between the antenna and ribbon and solved the problem. Hope this helps!