Then it sounds like the default spawn point is off. This is the command to move the default spawn point in a vanilla server:
https://minecraft.gamepedia.com/Commands/setworldspawn
Be aware that the default behaviour for spawn is this:
" If the server is not in adventure mode, players always spawn on the topmost block near ( x , z ) — y is effectively ignored. If the server is in adventure mode, then the new spawnpoint is exactly at the given coordinates, including the y coordinate (even if underground and even if there isn’t a block there) — if the y level given does not have space for the player then the spawnpoint moves up on the y axis until it does, at most y level 256."
Do this happend if you set up a new vanilla server? OR only after you copy in the world files?