There are many threads about issues when playing media from USB drives. I wanted to provide an update on my own experience with both a Model S and Model 3, so I’m posting it here in the General forum.
With my previous 2016 Model S85, I had frequent USB loading errors when listening to USB music. This issue started for me (and many others) with a software update from around April 2017 (I don’t know which version). The car would either hesitate while trying to start a new song and eventually recover, or just display a loading error with a refresh icon that could press repeatedly until eventually the song would play. While the car was having issues trying to play a song, other sounds in the car (turn signals etc.) could be muted. Some days I would have few or no errors; other days I would have many. Some people have no problems playing USB music, others have many. There have been several theories about possible causes, but none have been proven.
I took delivery of both a new Model S100D and a Model 3 last month. Both cars have issues playing from USB media, but not quite the same as before. Both cars reload the entire USB the majority of times you start the car, so you have to wait for that to finish before you can listen to USB music. If the USB doesn’t reload, it usually hesitates or fails to start playing when you start the car — you need to switch to USB and select something to play. I’ve had loading errors when starting to play USB music in both cars. Once you successfully start playing from USB, no more errors occur for the rest of that trip.
So, USB playback is still an issue in new cars, though the symptoms are a bit different.