1.12.2 Chunk unload method is unreliable?

I have been trying to unload chunks by looping through them and doing chunk.unload(false), as far as I know they do not unload if there are spawn chunks or players near them, but I have disabled spawn chunks and there are no players in the world, yet the chunks don't always get unloaded,

for example I have to unload all chunks every few ticks for 1-40 times until the chunks really get unloaded, the amount of times I need to do this seems random, sometimes I can do it instantly, sometimes after many tries

what could be keeping the chunks from getting unloaded? is there any way to forcefully unload them no matter what without unloading the whole world?

 

I found it to be caused by FastAsyncWorldEdit, problem solved, thanks to all who helped