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Teleporting to the nearest surface is a safety feature to prevent players from becoming trapped under the map, so there is a high chance that the nearest island was indeed the central one. Was the teleportation instant or did you see a loading screen before arriving on the central island?
With regards to the life raft, were you in shallow water? or is it possible a shark grabbed you and dragged you under?
The team are aware of an issue with sharks dragging players under the map, however, if your character glitched through without a shark pulling you, it would be good to know how close the ocean floor was when this occured. The raft being lost could possible be due to it gltiching too, and not teleporting.
Please let me know if there is any extra information you can recall of your experience as it will help me to narrow down if this is related to a known issue, or if it is new one.