Since 2017, numerous Microsoft Surface Pro 4 users face the sudden death of their Type Cover. There are tantalizing hints that the Type Covers went dead upon a Microsoft software update: 'surface type cover filter device' driver disappeared, and the type cover no longer works. 

Users around the world tried to revive their type covers using the methods advised by Microsoft to no avail. It’s absolutely unacceptable that a product turned faulty of no fault of the users and the manufacturer (Microsoft) isn’t answering questions.

We hereby request Microsoft to issue an official statement to this unfortunate incident and pledge to rectify the situation. It has been nearly two years. We have been patiently waiting but no more. It’s your turn to act, Microsoft. 

https://answers.microsoft.com/en-us/surface/forum/surfaccesso-surfkeyboard/surface-pro-4-jul-2017-update-type-cover-not/1c188925-c234-4369-8c93-af74417534d1