Ah, never really used folders but in retrospect it does sound like a cool feature.
Missing songs for me was like 1 to 2%, and usually relatively easy to solve by looking for the songs myself. Some songs were different versions, but that's probably less than 1%.
Not disputing it's buggy for you. It's not buggy for me though. Using it on my android phone, AAOS in the car, android TV, and two windows machines.
The only thing not working properly for me is the Yamaha Musicast implementation, and ofcourse their stupid refusal to let me choose my own language for the app.