Well, I merely tried what you said. There is a WaterMeshActor (automatically placed) that renders the water to be visible - and it was incompatible with multiple landscapes and/or World Composition back in UE4.
(On the other-hand Landmass works perfectly with multiple landscapes… only if we could at least hack water plugin to act like that… multiple landscapes would be a nice solution for me especially with world partition combined.)
I have tried making a “smaller world” and extending it when necessary, but when you extend an existing Landscape your Landmass/Water plugin’s created actors no longer function. I found a related PR: https://github.com/EpicGames/UnrealEngine/pull/8071
This MIGHT fix that issue, however if the landscape size one day grows too big, “extending a smaller world” is not a viable solution either.
I really do not want to go back to my original plan… (Initially I wanted multiple levels, but “inserting them together” is a hell, also making a World Map GUI is hell for that as well… so the “one big world” would be the best solution for geographical geometry reasons…)
… anyway please keep me updated in this thread if you find something. I will if I find something as well, however this thread is a bit of a last ditch resort for myself. I usually fix things for myself without help… 