Before anyone gets too excited: some of their electrodes are no longer able to record a signal from the patient's brain. They're reprogramming their software to work with fewer electrodes. No one is being turned into a borg drone.
Do you mean with the Voyager FDS? There's a big difference between patching a system 30+ years past it's planned mission date because at everyone's amazement it just keeps going and being valuable versus the Neuralink developing issues a few months after being installed when many expected it to fail because of the news of high failure rate among the primate test subjects beforehand.
I don't know. Even if the outcome is just that the implant just stop working, with no other issue, it's looking pretty bad to me.
Since it required literal brain surgery just to be installed, which I assume is already a serious risk, it's not something you want to potentially be useless.
All of them. The body doesn't want foreign materials inside it at any point. You can't just jam wires into your body and expect your immune system to not attack it. The organ interface problem as far as I know has never been solved.