Maybe, since it's only custom maps, you turned ocean on but you have it soo high that it covers the whole map. So instead of just water where you want water to be it is over the whole map. Try going into feralheart map maker, loading the feralheart map maker and turning off the ocean setting, then after saving it, go back into normal online feralheart, going into the map you edited and seeing if anything changed. (sorry probably very confusing).
hope i helped.