This was caused by rB0d73d5c1a2, which releases the scene mutex during kernel
loading. However, the reset mutex was still held, which can cause a deadlock
if another thread tries to reset the session, since it will acquire the
released scene mutex and then wait for the reset mutex.
Turns out there's no point in keeping the reset mutex locked after the delayed
reset section, so now we just release it earlier, which resolves the deadlock.
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