Hi Ben.
We regret for the inconvenience caused.
Do Not Disturb Mode works to silence unnecessary notifications while you run almost any application in fullscreen. Each time you open an application in fullscreen, Do Not Disturb Mode automatically detects it and adds it to a list of applications. You can also add applications manually. To manually add the game application to the list:
Open the AVG user interface.
Click Menu ▸ Do Not Disturb Mode.
Click Add A New App, then select an app from the pre-defined list. If your chosen app does not appear on the pre-defined list, click Select App Path, navigate to the app's location, then click Open.
Click Close to confirm.
If the issue persists, please share a screenshot of the pop up from AVG.
Every 5 minutes, I get "Process C:\Program Files (x86)\AVG\Antivirus\AVGSvc.exe (process ID:2976) reset policy scheme from {a long string} to {another long string} and it minimizes fullscreen games I'm playing, or simply makes inactive the windows I have that are windowed-mode. This has been happening for about a month or two. Does anyone have advice? I would love to play games without this major inconvenience.
I apologize for the experience, Ben.
Please share us the screenshot of the AVG pop by clicking on 'see details'. You can post the screenshot here in your topic. Click on "Answer" & then click on the "Image" [mountain symbol] & follow the instructions.
Also, reinstall Do Not Disturb component and monitor if it minimizes the game window.
Refer the article for the same https://support.avg.com/SupportArticleView?l=en&urlName=Add-remove-AVG-Antivirus-components&supportType=home
That unfortunately did not stop it 
the game I'm playing, Star Wars the Old Republic, wasl already on the DND list but it has happened three times so far this evening.