Having played on PSO2 on JPN a few years back, one of the details I liked was how dynamic the boss themes can be depending on the situation (Vol Dragon burrowing, Boss staggers, etc). However, I immediately noticed that the music at times do not transition properly, if not abruptly interrupt each other noticably.
Zeshiraider for example, has different pitches and tempo to the music when it's laying down, staggered on it's back, or spinning. All of this is absent on the NA verison and instead just repeats the same theme from the beginning
This is also the case for Vol Dragon, and possibly other bosses.