I don't know if I'm the only one, but all of Yungs better structures seem to be spawning too frequently. (Including the Nether Fortresses which seem to be spawning almost next to each other)

Does anyone have a solution?

Perhaps another mod you have is affecting all structure spawn rates somehow? They should spawn fairly far away from each other, I believe further than vanilla fortresses. You can always use a datapack to make them rarer if you like.