Hello,
so I just recently started using this so there might be a lot of things I don't know yet, so bear with me 
so after some trial and error I created a new world, totally flat with only 1 layer of sand. this was because I wanted to make my own skyblock map but my own pc can't handle it, being both the host and the player at the same time.
at first it worked, I managed to join, put myself in gamemode 1, placed a block on top of it what made all the sand fall. I could first build a bit up while the sand would fall, slowly the lag increased, and after a while I timed out. when I wanted to join back again the server said someone else was already online (of the 1 player possible to be online, and that is me because it is whitelisted) and whenever I tried to join I kept timing out. I stopped the server and then started it again, but I was never able to join the server. the console seemed to be empty. I made it so 2 people could be online at the same time, and then it said 0 people were online, but I still wasn't able to join and kept getting the message that I timed out. now I added a new map (same principal with only a layer of sand) but I am not able to join at all.
I got the map by creating it in singleplayer first. the first map I created I hadn't done anything on yet, and the second time I hoped to get around the problem by first placing a block so the sand would fall before I placed it on the server, but this didn't seem to help.
does anyone know either how to fix this or if there is another way to make a skyblocks map (with pixelmon).
the log will be placed on the comment below since the message will be to long otherwise.
thank you in advance,
greetings,
EdKroketje