I’m almost sure there is being some incompatibility into Norton and AVG (even like secondary, not residents) and avast. Or, on contrary, avast (as secondary) and one of the others like main.
For secondary (backup, non-resident) antivirus, I suggest BitDefender Free and AntiVir (free). Both of them works perfectly with avast at main one. Otherwise, there are known problems with Norton and AVG 