I don't know. It must have been a topic or topics on the Equalizer APO forum where most users end up.
More info on such topics on antivirus software: Antivirus software may sandbox Equalizer APO at installation. I've only see that once on the Equalizer APO forum however Peace was sandboxed also once or twice. And Equalizer APO suddenly stopping as the registry keys it creates/checks were blocked by such antivirus software. This happened quite suddenly due to an update of the antivirus software. Sorry, that I can't remember what brands (besides its not stated usually). On the other hand, I saw once a topic of user which had an issue on the config.txt file of Equalizer APO. This file is the most important of them all. Interfaces for Equalizer APO like its Configuration Editor or HeSuVi writes to this file or in the case of Peace to peace.txt. Some antivirus software suddenly decided to block writing or creating of config.txt. Maybe because it blocked writing to the c:\program files folder or their subfolders. After granting access access to c:\program files\equalizerapo in the antivirus software Equalizer APO starting working again.
I say the above as antivirus software could intervene (check) with the Equalizer APO process slowing things down. So in short: registry writing/reading of Equalizer APO, creating/writing config.txt or other files in c:\program files\equalizerapo\config and sandboxing (although at installation so not in your case).
