[ReshiramZekrom]

Well, there's a SA limit for pickups: they don't show if the map is too far from San Andreas. I don't know the exactly position since they start to don't show, but I have the confirmation that they are shown in the sea but only if the map isn't really far. You can try with this tool to get close the map to San Andreas. Maybe, by doing that, also checkpoints will work properly