I can’t envision this is a FOG related issue. But, if you sysprep an image and then reboot it on the same machine (removing fog from the picture) do you still have keyboard and mouse function?
I would tend to think its a driver issue where you started with an earlier release of windows and its drivers, upgraded to 1803. Maybe the earlier windows drivers were still intact and then when you sysprep all of those drivers are reset to 1803. Understand this is just a guess. Also watch the revisions of your firmware to see if there is an update that solves your issue.