McAfee FullScan on Mac stops in the middle of scanning

Recently downloaded AT&T Internet Security suite for Mac powered by McAfee, running on High Sierra 10.13.6.

When I manually start a FullScan, it always ends up with a message Scanning stopped. No response from scanners.

I repeated this more than a few times, and got the same failure every time. Then I watched how the scanning goes (as all of the menu items under "History & Log" are all dimmed out and it didn't indicate if there was any detail log file. Sigh!) 

The scanning effectively halts (or starts to wait forever) when it tries to scan /private/var/folders/vx/wp827ch...ok_Metadata_.MetaData.lock_lock. This seems to be a lock file implementing a semaphore, so it seems unlikely that McAfee will gain an access even if it tries to get an access for a very long time. Apparently a bug.

Did anyone encounter this problem? I tried to see if I can change the preference such that scanning of the subfolder can be skipped, but /private is not even listed on the pop-up folder selection box for exclusion.