comodo starts blocking "windows operating system process.
"Windows Operating System" is the destination for inbound packets that don't have an explicit application listening for those packets. Since you're describing this in the context of a VPN, I would suspect that your VPN isn't completely configured. Most VPN's have background protocols in use that help control error correction and routing information, and if those are not set up just so, things may work, but not very well. Not knowing what kind of VPN you are using, I can't tell you much else.