I was on my computer tonight and went to cancel the scheduled scan Avast was doing when I realised the Behaviour Shield was disabled and could not be re-enabled. I tried seemingly everything. Restarting, repairing, even a clean install and it still isn’t letting me enable it. On a side note, when I go to disable all shields and re-enable them the Anti-Rootkit and Anti-Exploit also can’t be re-enabled, although this isn’t a problem as long as I don’t disable the shields. I have Avast Free Antivirus and the version is 20.2.2401 (build 20.2.5130.571).
UPDATE
New Avast update fixed my problem (v.20.3). If you have the same problem as I did, try checking for updates.