On 18 December 2022, a Boeing 777-200 which had just departed Kahului in IMC had reached 2,100 feet over the sea in cloud when it began to descend in response to flight control inputs without the Captain as pilot flying recognising what was occurring. Recognition and recovery was slow and only prompted by a combination of EGPWS and verbal PULL UP warnings from the First Officer with a high speed descent to within less than 800 feet of the sea surface. The occurrence was not reported - nor apparently required to be - and the Investigation scope was thereby significantly compromised.