Did you install [https://www.coconut-flavour.com/coconutbattery/|CoconutBattery] app so you can see what’s happening? If not let’s do that and post a snapshot of the Apps main window so we can see what’s happening as well with the charger plugged in.
As far as the cable cover screw as seen in Step 5 in this guide [guide|135502] as long as you got the one screw in the plate should be OK, even still you should get a replacement screw just make sure it’s not floating inside.