looks like a graphical issue.
it is either with your configuration or your computer.
if it is your configuration:
make sure that your view mode on the composition is not in wire frame mode.
if you have cameras placed anywhere make sure you aren’t viewing those.
check your settings and if none of those work…
reset after effects settings to default, and see how it goes from there.
if its a problem with your computer:
check your gpu drivers, restart after effects, and restart your computer.
im guessing you dont want to re-install ae, but that could fix it.
good luck, thats all i can do to help.
“being 13 is a good time to start vfx”
-jonachan chainy