This bears a very close resemblance to a moth called Physematia defloralis Strand, 1919, illustrated on p 258 of Wang & Speidel (2000) - Guide Book to Insects in Taiwan (vol. 19).
Strand described this originally as a variation / variety of P. concordalis (which I can't verify at the moment as the LepIndex is down). I don't know without seeing a specimen which of these two taxa the HK species will be attributable to, or if it is another species. Internet searches on both taxa came up blank. For the time being I'll refer to this as Physematia sp. nr. concordalis.