A surprising find when I was at Pulau Sepa Resort running a workshop! They were not there the first night, but the second day appeared and were roosting around the island and stayed for the duration of our time there. At night, very active and noisy. By day I would find pairs spread around the island like this, and found only one group (~25-30 individuals). Unclear if they are permanent or migratory. Could be vampyrus or hypomelanus, though I'm leaning vampyrus due to relative size and the mantle coloration (hence the ID). Couldn't get a good picture since everything was so backlit from the extra sunny days we got.
And yes there really is an island there but it's so small I can't get it to appear on any version of Google Map.