Idle full system scan runs when the computer is not idle

I have NA 2009 16.8.0.41 and the idle full system scan starts even if I am using my computer, and will not stop and resume as it is supposed to do. In the past, the scan would only run when idle, and if I interrupted it by using my computer, it would stop and then resume when idle again. Any ideas on what is happening? Thanks in advance.