This issue isn't specific to Hamlet. I will often get disconnected islands in my RoG worlds with no Wormholes connecting them to the mainland, making them completely inaccessible. I know that this issue was fixed in Hamlet, but it still happens in RoG, Cave and Ruins worlds. It should be a relatively simple fix, as you could probably just use the same worldgen rule that makes disconnected islands in Hamlet require a wormhole.
Generate a large RoG world (works best if you set the size to 1000 or more in forest_map.lua) and reveal the map to (most likely) see a disconnected, inaccessible island.