Hello,
I have similar issues with Discord which also seem to be caused by the file system shield of Avast. Just like the thread OP, those issues only occur after a while.
In my case, notifications will display immediately, but sound is delayed by one or two seconds, and Discord consumes one entire CPU core before the notification sound is heard.
Same CPU usage issues if I disable or enable microphone or speakers on Discord.
And if I close Discord and reopen it when those problems occur, startup is much longer and CPU usage is much higher.
As of yet, no solution besides disabling the file system shield (or the whole antivirus).
Restarting the system solves the issue only temporarily. Reinstalling or repairing did not solve the issue.
It seems to be a conflict between how Discord interacts with the sound interface and Avast, though it may also be due to a conflict with a sound-related system file.
Here my configuration:
Genuine Windows 10 version 1703 (Creators Update) x64
Intel Core i7 4710HQ w/ Intel HD 4600
GTX 850M
16GB RAM
Using Windows' firewall
No additional protection installed. Windows Defender fully disabled.