To me it sounds more like the device received too much current on it's driver circuit and shut down to prevent damage to the device which is exactly what an imp

To me it sounds more like the device received too much current on it's driver circuit and shut down to prevent damage to the device which is exactly what an implant should do since shutting down just means a trip to your doctor to get it (wirelessly) turned back on as opposed to dangerous and costly brain surgery to replace it. These isn't a lot you can do about this sort of problem. The electrode used to stimulate is the main entry point for RF interference and you can't shield it for 3 reasons. 1)It adds size. You are effectively stabbing yourself in the brain with a coat hanger. Smaller is inherently better. 2)It adds mass. The difference in mass between a brain implant and your brain itself leads to brain damage in high kinetic situations like car accidents due to the different rates of acceleration. 3)Shielding an electrical stimulator prevents it from electrically stimulating thus defeating the purpose of the implant in the first place. What you probably need is a robust RF limiting front end to protect the device from unintended signals which is a major design challenge depending on the nature of the stimulating signal and permissible heating.