Skyblock server generating world chunks

I had this problem for a while when I play regular skyblock with friends then the next day, the server generated world chunks, at first I thought this was a glitch so I restarted the server, but it still there so I ended up creating a new server, then when I joined the new server, I immediately logged out, restarted the server, rejoined and found that no world chunks was generated, I thought I fixed it but then the next day the same thing happened and the world generated these chunks. I had the optimize option on and I am completely out of ideas on how to fix this.