cant open my world

hi moderators, i have a problem with my world, i've tried so many times to open it with tutorials in youtube and it wont fix this problem, i passed the world from server to single player and still wont open.

in multyplayer when i try to open it, somentimes it opens but the world doesnt load and you just fall and then the game crashes and says:

 io.netty.handler.timeout.readtimeout.Exempion

in single player the game says at downloading terrain and stays for there like 2 mins and then it says, crash reports and report mojang.

in multyplayer 2 friends tried to join the server but is the same to him
please help me, im creating an adventure map but this crash doesnt let me finish it