I'm having the exact same issue. My main browser is Firefox, so I tried running Hubspot in a private window, which should ignore any cache or cookie issues. That didn't work. I tried using Google Chrome, which I don't use, so no cache or cookie issues - same problem. I've gone so far as to blow out my cache and cookies on Firefox too, to no avail.
It is VERY slow. As in I type, then wait 30 seconds for everything I wrote to actually show up on the screen. This has been going on for a while now and happens on at least 2 different machines at the same location.