If both AVG and Windows Defender are running in the background at the same time, then I could see there would be conflicts.
So, don't do that. Install AVG and let it run continuously in the background with it's anti-virus and anti-spyware components.
Open Windows Defender and goto Tools then Options. Under "Automatic Scanning" remove the tick. This removes any scheduled scans. Then scroll down to where it says, "Use real-time protection (recommended)". Remove that tick. Click Save to save the new settings.
Now you have AVG running all the time in the background, and Windows Defender just sits there, unused, until you run it to perform manual scans as a double check.
Does that help?