You should identify a few things in order to figure out if that number if real or bogus and where is coming from. Login to command line and do a top command. Pay attention to load.
First, on a server with a real load like the one described by you it will be a delay from a few seconds to tens of minutes. If your router is responsive it is possible that the top result to be bogus.
Then take the number from top and dived it to the number of cpus.
To know how many CPUs your system are seeing do a
$ cat /proc/cpuinfo |grep ^processor
Usually the number of CPUs is the number of cores multiplied with the number of threads so what you see here should match with what you know about your hardware.
Then divide the load from top to the number of CPUs. This is the number you should see on ZS interface.
Let me know what you find.