/restart is a spigot script, and thus outside MineOS’s control. A quick google search reveals that several others also have problems with spigots restart script.
I cant, however, find someone with that exact description (or error message) that you describe.
The error message “sever condition not met !up” tells me that spigots restart script consists of two commands stop and start your server. Since /stop stops a minecraft server (and kills its java istnance) most of the script is handled in a spigot shells cript (I guess). This leads me to think that /restart fires of a shell command that first tries to stop your server, then to start it again. For some reason the stop command is not sending errors when it is ran, or it is possible not ran at all, so that when the script jumps to the start portion of the script it fails, since your server is all ready running. It is in a state the considers “up”, but it expects a state that equals “!up”, or “Not Up”.
I would take a look in your spigot directory to see if there is a script there called restart.sh or something like that, and to take a look at it’s script. Try to see what the script tries to do, and maybe try out the commands it tries to fire off to see where the script fails.