“Defeated” isn’t a recognized playlist atm. That said, when you do go down in a fight whatever battle track was playing immediately stops and a new one comes on when you get back up, which is a real problem.
Yes some boss fight music doesn’t play when it should during boss fights, in particular Giganticus Lupicus always has no music for the first 2 stages, then music starts and then stops at the beginning of the third stage. And you are right, it never randomizes even with a blank randomizer track at the top of the list.
Main Menu music also never randomizes. It’s always the same songs in the same order over and over again.
Jumping puzzles vary in what music plays. Sometimes, nothing. In the case of the Clock Tower, the same boss battle song from my custom playlist played every single time the puzzle reset. For the Wintersday jumping puzzle, the default Wintersday song played despite having a custom soundtrack installed. Similarly, certain story missions will have default songs play in some quest sequences regardless of your custom soundtrack.