Mouse and Keyboard Not Working After Recent Software Update

It sounds like something is confusing the OS.

Since rebooting your Mac doesn’t fix things, see if the problem still happens in Safe mode (press the shift key when you hear the startup chime at startup, hold until you see the Apple logo and progress bar). It can take much longer to safe boot (10 min) so be patient.

How to use safe mode on your Mac - Apple Support 

Safe mode forces the OS to clear certain caches and logs and do other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's expected.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and re-evaluate the issue again.

If the problem is still unresolved, please return here and post a reply and we’ll see what else we can come up with for help.

Usually when both the Keyboard & Trackpad stop working at the same time on the 2015 MBPro it usually is due to a bad Trackpad Cable. The Trackpad Flex Cable on the 2015 MBPro has a high rate of failure. If the Trackpad Cable is not the problem, then it can indicate an issue with either the Trackpad, Logic Board (or possibly the Keyboard).

Try booting into Internet Recovery Mode using Command + Option + R or from a bootable macOS USB installer to see if the Keyboard & Trackpad both work. If this works, then it may indicate a possible software issue with your macOS installation. Try to reinstall macOS over top of itself (without erasing the drive) using one of the methods just mentioned. You can also try booting into Safe Mode which if it works indicates a third party app is most likely causing the problem.

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