A new report has built on security fears reported last year that the wharf could be used as a naval base by China.
The concerns came in a recent review of China's Belt and Road initiative by researchers at thinktank the Center for a New American Security.
Scrutiny of the China-funded wharf revamp in Luganville last year prompted Vanuatu to strongly deny reports it could be taken over by Beijing.
Vanuatu's government was also forced to disclose there was no debt-swap agreement in the deal.
But the Belt and Road report, released earlier this week, said the arrangement was still nontransparent, locally disengaged and geopolitically risky.
It added the wharf was financially unsustainable because of the relatively high two percent interest rate on a $US54 million loan.
A separate Belt and Road project reviewed by the researchers, the Port Vila Wharf in Vanuatu's capital, found no challenges present.