Internal keyboard stopped working for my MacBook Pro (Retina, 15-inch, Mid 2015) too. Same problem, from time to time it works, later it stopps workin. It's cold now, here in northern Argentina, and although in the morning when the MBP is cold it does not work. It does not seem a problem with heat. I upgraded to macOS Mojave 10.14.4 hoping that SMC gets reset. It worked for 1 week and stopped again.