What does it mean when, under the Status column, in the log, it says the scan failed numerous times during the scan?

I ran a manual deep scan, which only took about 70 minutes, and showed '0' infections; however the log shows several rows of AV/Treatments, under 'Type' and Scan Failed under 'Status', during the course of my manual scan. Why did the scan fail for some files and does that mean that those files have been scanned? Im not sure what all this means, could someone please help me? Thanks.