Hi all,
I'm recently buying LG F60 and when battery not too charge and smartphone shutdown, after charge and start smartphone, I have the same issue, vibration on Back, Home, Tasks button and when unlocking the phone. I found on these page : forum.xda-developers.com/android/help/lg-f60-d390n-t2930803/page18 a solution.
Download and install HapticSwitch, you found it on playstore, after installation, click one time to enable/disable vibration and a second time to disable/enable vibration, depending the state of vibration before.
Enjoy.