Emulator

If this game is like BMX XXX and Aggressive Inline, the audio interface will be configured to expect 48KHz input from the DSP instead of the usual 32KHz.

NHL Hitz 2002 seems to do the same thing. I really don't feel like making an issue report.

Any idea why this works on LLE but not HLE?

I'm guessing because HLE wasn't written to accomodate 48KHz output, because in the words of the GC SDK: "Currently, only 32KHz output from the DSP is supported. There are no plans to implement a 48KHz mixer in the DSP." Lies Ninty, lies I say!

AX UCode doesn't really care about sampling frequency. It outputs 5*32 samples at each "tick"/command list sent to it (unless I've missed a weird custom version). It's either a DSP emulation scheduling problem, a HW/DSP issue or an AI issue, in my opinion.

It works in LLE audio though?

Aggressive Inline writes 160 samples to AI every 3.25ms.
An ordinary AX game (I tested Prince of Persia) writes 160 samples every 5ms.
If the DSP is being run more often it must be resampling to a higher rate, so there is nowhere the fault could be other than in the HLE code.

That should probably be 3.33ms... sub-millisecond timing is problematic.
AFAICT the ucode in question is the one with ector crc 0x07f88145 (7968 bytes).