The mystery still hasn't been solved. Here some feedback I received recently by Dr. Mike Vecchione from the Smithsonian in DC, Washington:
"I have seen quite a few Macrotritopus and this does not look like any of them. In that genus the ventrolateral arms are much longer than any of the other arm pairs. It could be any of the long-arm species with shallow webs. There are many such in addition to Wunderpus."