provide exact Ae version full numbers and show us a clear screenshot of your full Ae interface with the black background, and with the transparent as it happens (take a screenshot of both). if you can video capture this behavior do so. this could be a user error, software or hardware failure. at this point we can't be sure without more information.
Thanks for replying! My Ae version is Adobe After Effects CC 2017 14.2, Could it have something to do with my disk cache folder because when I open Ae I recieve a message saying my disk cache folder doesn't have a safe amount of space for storage.
thanks for that helpful video.
first of all make sure you are using the latest update 14.2 you can check and see that under help->about after effects. this may or may not be related.
from looking at your setup I see you are viewing the left view and not the active camera.
change it to active camera and try again.
if that does not work, I would purge the cache: edit->purge->all
if that does not work I would reset my preview settings:
if that does not work I would restart the software and reset preferences when opening the software back, here's instructions:
come back with the results, we'll figure this out eventually
Thank you so much for your help! Changing left camera to active camera fixed the problem. Glad to know why this happens now, thanks again!