I'm on 20171227 firmware and I'm seeing that vibration acts erratically, which didn't do before.
I'm not using battery saving mode. When I unlock the phone, vibration doesn't work. If I'm using the keyboard, which I have set up to vibrate on every key press, it doesn't vibrate. After I've pressed some keys, it starts vibrating, but the vibration stops again if I stop touching the screen, and begins working again after some more key presses.
The same applies to the capacitive buttons and the fingerprint scanner. If I touch the back button, it doesn't usually vibrate. If I touch it several times in a row, it begins vibrating again and keeps vibrating, for as long as I keep touching it. If I stop touching the button, vibration stops working, but will work again after a few more touches of the button. If I lock the phone and unlock it right away with my fingers, the fingerprint scanner vibrates, but if I lock the phone and wait for a longer time to unlock it again, the fingerprint scanner doesn't trigger the vibration.
Could it be related to the solution implemented to solve the phone not entering deep sleep issue? Vibration worked like a charm on previous firmwares.