From experience, 20 servers on your spec is optimistic. You have to remember that if 2 servers crash you're pretty much out of CPU.
I am going to create a system to automatically detect and terminate out-of-control servers which are using 50% CPU.
It archives the autosave.bls file before terminating the process, then restarts the Blockland server after a few seconds.
The System_HamHost add-on will also keep sending the latest system time to the Java program. This way, a server which is using 50% but has 33 or so players on it will not be ended.
From my observations, a Blockland server with this CPU spamming error will not be on the master list, and you cannot connect to it.