So there are some things to give you guys a hint, what is going on.
Well I downloaded brand new unturned to my Ubuntu 16.04 LTS server, including mono version of 3.12.1 - that's version that unturned uses and console doesn't spit any errors about Runtime things.
Console right after running the start.sh script: http://prntscr.com/lk7gg0
Server doesn't decompile mods, you can join it but saves and none of the commands work.
And it shuts it self down after about 10-15 seconds.
File tree: http://prntscr.com/lk7h9m
I don't really know what the issue can be. Please help, all help is appreciated 🙂