My bad. This had to do with my App\ code.
For further reference, if you face a similar issue, a good place to start from is: http://php.net/manual/fr/function.debug-backtrace.php
I guessed I was calling a Service too soon in my Application lifecycle and wanted to know where.
This helped me figuring out where I was calling $app->make( ... )/app( ... )/ ... too soon in my Application lifecycle.
You shouldn't use the Container::make method before all your App services have been registered correctly.
Hope this helps.