Ideally its the bytes that was received after completion of a web request like GET. It looks like the variable which holds the received bytes value is not able to hold the large value correctly which is why we are seeing this incorrectly.
Will need more data to see why this is happening.
a) which IVE OS do you see this on?
b) You see this on your syslog data, do you also see the same value on your IVE's user access log as well?