I got a solution for my home made bundle:
The problem was coming from my routing.yml file (in app/config). I was using fosjsrouting and it seems that the routing of fosjsrouting needs to be called at the very end of the routing.yml file (in app/config).
See below:
app/config/routing.yml:
... and at the very end:
fos_js_routing: resource: "@FOSJsRoutingBundle/Resources/config/routing/routing.xml"
However, I still don't understand the problem with the coresphere bundle. This doesn't solve it.