When asking a question on the After Effects user-to-user forums, you can make it easier for folks to help you by proactively providing complete information.
IMPORTANT: Screenshots and sample movies are often very useful in showing exactly what you're seeing, and can thus make getting an answer faster and easier.
Also, please do everyone a favor and do a quick After Effects Community Help search to see if your question has been addressed already.
Be sure to answer all of these questions when asking for help:
What exact version of After Effects? To check that, visit this page.
What operating system? This should include specific minor version numbers, like "macOS v10.15.5"---not just "Mac".
If you are getting error message(s), what is the full text of the error message(s)?
What were you doing when the problem occurred? What is the exact sequence of steps that you are taking?
Has this ever worked before? If this worked before by doesn't work now, what has changed on your computer in the intervening time?
Tell us about your computer hardware. Include CPU type and number of processor cores, amount of RAM installed, GPU, number and sizes of connected monitors, number of disk drives, and how any external drives are connected.
What versions of drivers for your graphics hardware do you have installed (including CUDA driver and driver for display adapter)?
Do you have any third-party I/O hardware (e.g., AJA, Matrox, Blackmagic, MOTU)?
What kind(s) of source footage? When telling about your source footage, tell us about the codecs, not just the container types. For example, "H.264 in a .mov container", not just "QuickTime".
What other software are you running?
Do you have any third-party effects or codecs installed?