sync issue

A student has been hacking at a Vulkan engine and laying the foundation for future work. We're relatively new to using Vulkan. As we work on linux, mac, and windows machines, We're often bouncing between graphics cards and cpus. Everything is working fine on win/osx. Linux is where our problems are. On one machine nothing renders but frames are flying by at normal rates - you just can't see them. On another linux machine, every other frame takes 1s to render. This hints that we've a sync issue of some sort but we can't find it. Maybe you can help!

I have a gist of the main code on git hub here: https://gist.github.com/shaunramsey/1a746a4b8916fc79f62beb5a7cff8e78