Yes, I think it could have something to do with the amount of string tracking that needs to be coordinated with the actual picking motion. It may be something inherent to the technique, which would be quite ironic considering that DBX seems like the one tecnique that allows you to alternate pick anything.
The first pattern I learned was the classic four string ascending and descending loop. I was pretty excited when I realized that I could actually play it fast, but I quickly realized that it was the only thing I could do. Just starting on the highest string of the pattern (which reverses the pickstrokes) made everything fall apart.
In one of the Andy Wood interviews, Troy asks Andy to play exactly this pattern. Andy says he would start it with an upstroke (converting it back into the same picking pattern as if starting on the low string), and actually kind of struggles to start with a downstroke. So I don’t think we’re doing something wrong, this may simply be the way learning DBX works.
Anyway, the etude uses this pattern in a few places, so I’ve had an opportunity to practice it. In the last two or three days, I had a few good repetitions before losing the technique again. Today was the first time I could play it mostly consistently.
So while this kind of learning can be frustrating, it also feels great to see the progress, even in small increments. It’s also a completely different experience from the commonly taught “start slow, keep it clean and gradually speed up”, which never really got me anywhere.