Avast has a silent Gaming Mode. On your taskbar you can left click on arrow icon then right click on the avast icon and check mark it, but that still doesn't explain why it would change game play while you've left it running for 5 minutes( 14 year old 5 minute time).
Since it's been stated it's an online game leaving it idle may be causing you to have any others login and play thus being something on the servers end. In other words changing your place in line so to speak could be thousands. However I doubt it is. was just a thought.
This is one of those things that maybe can't be figured out or answered online. I'd make sure you have all the latest drivers
for your chipset, graphics card up to date.
Also make sure you have any patches available for the game installed.
Task manager is not showing all that many task running to cause this yet once again we're back to why does it happen when you leave the game idle.
Try doing the same thing only not leaving the room but monitoring task manager and heat.
Ping the server before and then 5 or so minutes later (as if you've left the room then returned) see if their is a difference How to Ping a Server Name | eHow.com
That's about all I've got on this one.