I have the same problem, also using unifi 5mps, direct cable.
Yesterday I was back in hometown and use my Yes4g wifi connection to play, dont have this problem at all.
I suspect its wifi vs cable issues, so I use unifi wifi instead of cable, seems fine a while but then problem came back.
Since my Yes4g no problem, with same settings(firewall, in-game console settings, etc), and both unifi wired and wireless doesnt, confirmed something in the router kacau with cs:go, since dota, etc are smooth.