Hello there. So I began playing this very large 12k x 12k map called drehmal v2 (https://www.planetminecraft.com/project/drehmal-v2-prim-rdial-12k-x-12k-survival-adventure-map/), with a small modpack and optifine on 1.15.2. I had no problems with it whatsoever, optifine with shaders and the mods working all perfectly. So I get some friends over so we can play this map together.
I give them the same mods and everything through a USB, and I create a new default world to test if the multiplayer works correctly. The three of us join the normal default minecraft world perfectly, all with shaders on, and the small modpack we all installed, everything is working fine. So assuming everything is fine, I start the large map I mentioned earlier. I load in fine, shaders and all, but now when my friends load through LAN they cannot see the terrain, and are floating in and endless sky. They can see other mobs, as well as each other, but cannot move and there is no terrain. I HAVE DONE EVERYTHING TO GET IT WORKING. updated forge, tried different versions tested other default worlds (leading me to believe the problem was the size of the downloaded map) etc.
I then tried to load into multiplayer with my friends with JUST OPTIFINE, NO FORGE. And everything was fine. We loaded into the massive downloaded world, shaders on and working, everyhting working fine. Then I try again with forge and the same endless sky scenario happens, so I have figured out the problem is with forge and the large nature of the world. (As previously mentioned everything worked fine on default minecraft worlds.)
I should also note that I tried loading it with an empty mods folder, and still got endless sky. So the problem is with forge, NOT the mods loaded by forge
Does anybody have a solution that will allow us to play MULTIPLAYER with forge and optifine on this massive map?