Make a bootable Memtest DVD or USB stick and run Memtest for at least 3 passes or overnight.A 15” 2014 MacBook Pro Retina (2.5GHz i7, 16GB, 500GB) has me stumped.
It won’t complete a Mojave install, and…
Under Mojave, Wi-Fi becomes so unstable as to render the computer useless.
In the past, this was a typical experience with RAM that was unable to perform to the standard required of it by the latest OS upgrade being installed. May be a long shot, but it does not take much time to set the test running and walk away.