According to a Thanh Nien report, a "composite inner wall window piece" would have been spotted by a Vietnamese marine police seaplane (the DHC-6?) at N473208 E1032226. The seaplane had to return [presumably due to nightfall.]
The coordinate must be erroneous, but the description is the most fitting so far. Let's see if it holds. The news item said "the pilot could take pictures, but not clearly".
Interesting. Finally some hard facts or at least some serious clues.
Can you please provide a link to this information?