Sophos Anti-Virus - Time Machine backup issue

So I've been looking through this message board and seen that this issue has arisen on several occasions and supposedly has been fixed, but I am still encountering issues with my system freezing on occasion during time machine backups if Sophos anti-virus is running.  My system does not lock up all the time - merely once a week on average - but this is still far too frequent for me to overlook.

I'm running the latest version of Sophos anti-virus (I believe) - 8.0.2C.  I also have excluded

/Volumes/My Passport/

/Volumes/MobileBackups/

/Users/Username/Google Drive/

from the on-access scanner, as well as excluding

/Library/Sophos Anti-Virus/

from my time machine backups.

I've noticed that occasionally my time machine backups are unusually large considering the amount of work that I've done since the last backup.  For example, if I take my computer home for the night and don't even use it, then plug in my external hard drive the next morning, time machine will do a backup of several hundred MB despite the fact that I've done nothing on the computer and I've excluded the Sophos Anti-Virus folder from my backups.

I've also noticed that since I have installed Sophos anti-virus, the amount of time it takes Time Machine to prepare a backup has increased drastically.  Whereas the amount of time to prepare a standard hourly backup for used to take no more than a minute, with Sophos anti-virus installed, the amount of time has increased to greater than 5 minutes.

I can definitively state that Sophos anti-virus is the cause of these issues, as I have tried uninstalling Sophos anti-virus for several days and the length of time to prepare time machine backups and the size of the time machine backups returned to what I had grown accustomed to before installing Sophos anti-virus (<1 minute and ~2-5 MB).

If anyone can help me understand what is causing these issues or help me find a work around to get Sophos anti-virus to play nicely with Time Machine, I would greatly appreciate it.

Charles