Maybe there's a case of "scan only modified files"? There are several antivirus software that do this, since I use bitdefender I can tell you for sure that bitdefender has such a thing.
I heard the same thing about kaspersky, but I wouldn't know for sure because I had some problems with it a while ago and I'm not using it anymore.
You should access your logs from AVG and see if the scanner has reported the rest of 27.000 files as unmodified
Avg has scanned 31,000 objects instead of the usual 58,000 during the last two scans.
Anyone had the same problem? Anyone got a fix for it? I haven't tampered with the settings.