The stick was 3.0. I just loaded a new stick with 18.1 gb of music. Once it loaded (which took about two minutes) it played everything without stalling. Unfortunately, it seems the stick has to reload every time you start the car.
However, the new stick was about 1/4" longer than the old stick, and it was a real struggle plugging it in. It's a very poor placement, and you really need to use one of the tiny thumb sticks, especially if you want to use multiple sticks to keep a large music collection at hand. (I only put about 50 of our 1,288 albums on this stick.)
However, the album art comes up very cleanly on the Pilot Screen, and it's easy to scroll and make selections (at least when parked). I tried Alexa to see if it would locate music on the disc, but no luck. So making a selection while driving is going to be a major distraction -- it means opening the media tab, pulling it down to the Pilot Screen, then scrolling through the menu to find what you want. That's a lot of eyes-off-the-road time. I'll only use the USB stick when I can't get a cell signal with enough bandwidth for music streaming -- which is a good portion of our local driving.
But the lossless files deliver great (non-Atmos) sound, and we'll be spared the long dead spells we've been sitting through.