What operating system are you using?
Windows 10 64-bit
Use an earlier version of After Effects. As usual, there are many bugs in the newest version. Wait for the SECOND bug fix before you use it again. Typically, the FIRST bug fix solves many common problems, but it also breaks features that worked just fine. The SECOND bug fix fixes the problems caused by the FIRST bug fix.
Then there will probably be a third bug fix, which addresses more exotic problems. But by then, it will soon be time for a new version. And the process starts all over again.
What antivirus software are you running?
Have you tried uninstalling and reinstalling?