Rendering blocks out my lower video track

[BrandonS_MD]

Hi,

I was learning how to create MOGRTS in AE today and followed step by step video (https://www.youtube.com/watch?v=fWH1QxbwsHI) on how to create a very basic MOGRT.  But when I did a quick sample video and popped it in my sequence, my MOGRT blocks out my video.  But when I scrub through the video, it works as it should (ignore the poorly designed white letters on white background for a moment).  I did not create a background solid in AE -- it was just the small rectangle shape and text layers.  

Pic 1 is of me scrubbing through the timeline, pic 2 is when I'm not scrubbing, and pic 3 is after rendering.  I didn't post it but I exported just to see if it still worked and it didn't.  Anyone know what's up?

I have a new Dell XPS (bought this past black friday) and it's specs are solid.  The graphics card is NVIDEA GEFORCE RTX 2070 Super, and I was forced to download its driver before opening AE.  

  

Anyone know what's going on?  And if you know, please walk me through your solution.  I thought I was fairly confident in Premiere but this one is puzzling me.

thanks!

Brandon

[BrandonS_MD]

POSSIBLE SOLUTION FOUND (but follow-up questions are below)

So I dug through the forum and saw someone else saying they had playback issues and tried switching the Renderer Engine to "Mercury...Software Only" which previously it was on the CUDA one by default.    I tried that, but no change.  I then deleted all of my render files (Sequence>Delete Render Files) and I started to see my video before I even scrubbed.  I rendered and it appears to be working fine.

So that leads me to ask:  If that is the solution, what is the purpose of the other Renderers (CUDA, OpenCL)? 

In my previous instances of using Premiere, I always assumed my weaker computers didn't have the graphics cards to handle CUDA or OpenCL, that is assuming those were more powerful renderers.  My current graphics card is a beast with 8Gb of video RAM (or whatever you call it), so I assumed the problem resolution was elsewhere.