When deriving the rough Bergomi model, Bayer et al in "Pricing Under Rough Volatility" (2015) perform a change of measure to ensure the price process is a martingale as shown in the screenshot below:
However, there is recent academic work, such as the "On the martingale property in the rough Bergomi model" by Gassiat in 2019, showing that the process is a local martingale and a true martingale under certain conditions as shown in the screenshot below:
I don't understand how, under the risk neutral measure, the price process is a martingale and yet current work says it's an unanswered question.