Yes, give us more information. We don't even know what version of AE you're running. (We'd need the version number down to the last decimal, for example: 11.0.4 or 220.127.116.11, or 13.0.0)
Also of great interest would be the origin of the footage you're using. Format, codec, etc. And whether you've been able to work in AE before.
AE CC version 12.2.1.
the footage was originally ACHD converted to prores 422 .mov
I thought perhaps this strange anomaly was fairly common and might have a simple solution. Sorry for lack of info.
Have you shut down your machine recently and then rebooted it?
Does it happen when you just have a solid and no footage?
Does this happen in RAM preview or just final render?
Has this worked before or is this your first time using AE?
Have you installed any codec packs recently (such as K-Lite)?
Also, click the link in my last post and answer those questions too.
I have not tried just rebooting it.
Happens only with footage.
Happens in both RAM preview and the final render.
Worked fine this morning. Been using AE for years.
No codec packs.
Previous questions answered above. Thanks for taking the time.
Try rebooting your machine.
Hopefully it's just one of those weird things that happens when a computer hasn't been turned completely off in a while.
Does it happen on any footage or just this one clip?
Also, not all of these questions were answered yet. We know nothing about your computer system, OS, etc.
If it worked fine previously and doesn't work now, something has changed. Did your OS update itself?