Scan looks like it has failed

The scan runs until it has scanned around 6MB to 8MB of data, and then it seems to hang. Eventually I get the “Scan looks like it has failed” message, and the last record in the log looks something like this (as an example)
[Mar 31 13:08:41] Scanning: /var/www/vhosts/*******.**/httpdocs/wp-content/plugins/****/****/*****.php (Mem:6.0M)

I support another website with the same host, the scans run fine, and there is no “Mem:6.0M” at the end of the file names. Do you know where the “Mem:6.0” is coming from?

Any idea how to proceed?