My server refused to update last night(after force update) and then i recreated the instance. but now it does not want to install umod so i cant use any plugins.
I had problems with this too. I found that I had to open the ports that Rust uses with ufw allow, then ufw enable, and this can be issue with other games as well. All depends on your hosting provider really.
I find that with umod you have to stop the instance and stop the server. Then start the instance again and push the update button. It normally took me at least two times of stops and restarts before it fully installed umod.