Sorry for my bad English.
Log of Firewall in AvastIS.
When running µTorrent, you can not view log of FireWall.
Log of FireWall can not load to view it.
Similar occurs when watching videos on Youtube.
If you close all active network programs, the log of FireWall after a while you can see, and the function is available to clean it.
After clear the FireWall and run µTorrent, after two or three minutes again it becomes impossible to view a log of firewall.
Conclusion: When the active network firewall programs magazine periodically updated with new records, and (log firewall) again rewritten and re-opened.