perhaps ro bin being in shipwrecked at all is a bug in itself, since chester and packim' cant leave their worlds, but if youre moving too fast in the water, ro bin gets stuck, and to get her unstuck you have to go out and get close to her again until she follows you. ive noticed she always gets stuck right in the middle of a colour change.
another thing is, upon starting up the game, ro bin flew off, and i was so confused as to why that i went godmode and followed her. turns out, if you leave the gizzard stone on the ground, exit, then reload, ro bin goes off to find the fishbone to latch on to instead. picking up both the bone and stone doesnt equal in both ro bin and packim', and neither does reloading the game, though ro bin will follow both the stone and bone.
i decided to test this out in a separate save, and it seems like ro bin overrides chesters and packims spots to the point she goes off to find the others bones, which isnt exactly ideal in an unexplored world like shipwrecked. and if you leave ro in hamlet, load in packim, then bring ro bin back to shipwrecked, packim disappears completely. and if you keep going back and forth between the same two worlds quickly, ro bin runs off too, despite both items being with you; though this can be fixed by going back to hamlet.
sorry this is such a mouth full, i was just so confused as to why ro bin just. flew off. thank you, i hope this helps!
take ro bin from hamlet to shipwrecked, drop the stone on the ground, reload, follow her