I had freezes in game lasting several seconds(maybe my game would crash if my computer was low end, maybe it did crash but rarely so i don't recall), fixed by checking windows event viewer, and i've noticed at the time the game acted weirdly that there was some service i think lsass.exe that was being blocked by my firewall, unblocked that, and everything went smooth from then forward. Bnet is using some services to connect not just agent.exe or however it is called.
So, check event viewer or just reset your firewall entirely. Google if need further help with this.