Becomes very, very obvious when listening to the music while Beat Rumble is enabled. The offbeats are actually closer to the rumble than the actual beat is! (If the music runs at ~460 ms per beat, it feels like the desync is about 150 ms.)
This occurs for both the Future Hyrule dungeon in the regular story, and the overworld music in Symphony of the Mask, indicating that something is wrong with the sync of the track itself. It seems like other tracks are unaffected, though I didn’t check them all thoroughly.
Sadly this one bug makes Symphony of the Mask infuriating to play, especially with the increased difficulty of the enemies around and seemingly random missed beats occurring every ~10 beats or so. In particular, I found it impossible to open any of the flawless purple chests until I turned the music off and beat rumble on.
A very hacky workaround for this was accidentally(?) found by SpootyBiscuit (and others?) by deliberately incorrectly calibrating for latency. (Specifically, the average Switch latency appears to be about 50-100 ms, so ignoring latency calibration altogether and setting it to 0 ms ends up making the sync better due to the bug.) Of course, this desyncs all other tracks by the ~same amount in the opposite direction. “Splitting the difference” like this can make the game just playable again for a very accurate player. I imagine this workaround would be non-functional on Double Time mode.
In particular, if this almost-game-breaking bug (it’s game-breaking for a rhythm game) could be fixed before the physical version locks it in forever next month, that would be hugely appreciated!