Put the summary of the bug you're having here
If I add a flat present to the server config, chrange generator to FLAT, restart server and go to not generated chuncks Thay will be as in server config is not any flat present 3;1*minecraft:bedrock,254*minecraft:stone,1*minecraft:bedrock;2;

What I expected to happen was...:
The same as when you chose the present in singleplayer

Steps to Reproduce:
1. crange generator to FLAT
2. generate a bit of world
3;. add a generator setting to the generator-settings line
4.restart server
5. there will be \: instead : symbols
6. go on the server
7. go wery far avay, where aren´t generated chunck