The default Jobe server is just a small 2-core server intended only for system admins to check out their install of the CodeRunner plugin. To quote from the documentation:
In its initial configuration, CodeRunner is set to use a University of Canterbury Jobe server to run jobs. You are welcome to use this during initial testing, but it is not intended for production use. Authentication and authorisation on that server is via an API-key and the default API-key given with CodeRunner imposes a limit of 100 per hour over all clients using that key, worldwide. If you decide that CodeRunner is useful to you, please set up your own Jobe sandbox as described in Sandbox configuration below.
So if you do continue to use the default server, you're liable to intermittently be told that the submission limit has been reached. This not only prevents you and your students from using that Jobe server but also locks out anyone else in the world trying to use it, until the next hour.
I am just a university lecturer who has developed some software. I'm happy to make it available free and open source, but I'm not offering a computing service. There are close on 2000 registered Moodle sites using CodeRunner, some with massive student enrolments. Neither I nor my University can provide computing services to a user base of this scale.