Thank you. It helps to me.
Additional information:
Bitcomet 1.36 x64
Internet connection - L2TP Up to 80 Mbps
The problem manifests as a router (Zyxel Keenetic with latest firmware), and without it
Windows XP x64 with all updates. Internal Windows firewall with Webroot Secure Anywhere Antivirus + Dr. Web Cure it! weekly check.