Apple might have been 5 years away from the development of their iPhone 6S and 6S Plus, but that does nothing to prevent them from offering support for the devices. That is why the company is currently starting a service program for a select few of these units which could fall victim to an unexpected shutting down problem.
According to the Cupertino-based company, not all users of the said units will suffer from this problem. It is apparently an issue with those which were manufactured between October 2018 and August 2019 alone. In fact, they have provided an official serial number checker on their website where you can check to see if your unit is one of the problem devices.
Apple has also made it such that you don’t have to wait for the said component to fail before taking action. They advise reaching out to an Apple Authorized Service Provider, going to an Apple Retail Store or checking with Apple Support to see if you can send the phone to them via mail. Likewise, Apple offers to refund users who have had this problem in the past and had to fix it themselves.
Unsurprisingly, the company has failed to mention which components might fail to cause this problem, neither have they detailed the servicing guidelines to get it back up.