I would suggest trying 1.4. A lot of major performance and stability
fixes were added.
If you strip your configuration and just add your 168 contacts do you
still get the problem. If so just open a case on the Shinken github and
copy your configuration.
Jean should be able to quickly fix it as this is a core issue.
As to scalability, unless you hit an odd bug or a known bug, you should
Also make sure to follow the guidelines. (All same python version, same
pyro version on all hosts running Shinken).
Good luck, Shinken is an interesting beast that has lots of potential.