So I'm thinking that when an ADS-B system is malfunctioning, being tested, or perhaps being calibrated a lat lon of 0/0 is common.
That would explain why all of these birds stack on top of each other. I do not believe they are actually at this coordinate nor do I believe there is a secret island there.
If there was a hazard to navigation such as an island, it would be on all modern navigational charts that ships use and it is not.