Goncalo,
It often helps me to "walk away" from a lesson for a day or two if I can't get the progress I want. Make certain you are counting out loud and keeping up with your counting speed. Forget about the play along track until you can get through the practice and count everything. It may help you to intentionally get side tracked with Circle of 5th practice or do some licks or speed exercises, ect.. Perhaps my method will help you, too. Like I said, just don't concentrate so hard on it for a day or two. Come back and I'm betting you'll do better.