Hey, just installed 3.0 release and noticed that after I open connection to ROS with winbox I got a 16-17mbit/s load.
Does anyone have the same problems?

Strange, but now (after ~1hr uptime) it works like it should.
But when that happened only window open was "Interfaces".

Try this: Logout and then log back in after un-checking the 'Load Previous Session' box in the winbox loader.

I think a clean session may help.

Also make sure you are running the latest version of winbox.