After fighting with this for a while, I felt it fair to post something about this here.
When I got my AtomicPi and first set it up and started testing, things seemed pretty good. As I had more time I started testing out video playback on the system.
In this time I had a v1 and a v2 wiring harness I had made, with the second being much better (will try to provide some images at a later time). I mention this because in my testing, my first response was to assume it was being under powered.
Anytime you would playback video on full screen with VLC specifically you would hit a point, be it 5 minutes in or maybe even an hour in where all the sudden the system would reboot. No warning, no information in the logs (/var/log/{kern.log,syslog}) just a hard reboot all the sudden. After testing all the different playback options, I noticed that GnomeMPV and MPV would playback video at full screen, no issue and I couldn't find any other related information.
Finally, I did finally locate one piece of information about information about the issue, but it just sent me down a rabbit hole:
Apr 30 01:05:26 localhost kernel: [ 1312.380332] [drm:intel_pipe_update_end [i915]] ERROR Atomic update failure on pipe C (start=79683 end=79684) time 272 us, min 1073, max 1079, scanline start 1062, end 1081
Which if to be believed indicates an issue with the i915 chipset drivers used to power things here. I tested all the grub changes, and different suggestions (bar building a new kernel my self) and this kept replicating.
Now, all this said... I will TL;DR;
Move to Ubuntu 18.10 release as quickly as you can, the kernel in the 18.04 release is buggy and especially has issues with the video implementation. After spending forever trying to fix it, moved on to the newer 18.10 and newer 4.18.20 kernel series and this seems to be resolved and things operate normally.
So far things have been much much more stable. Hoping this save someone who comes across this post some time and some hair (from pulling it out as I have).
Cheers!