In Platform Designer, Generate HDL fails for a hierarchical system that's two levels deep, but succeeds when the hierarchy is only one level.

I have a hierarchical Platform Designer system (e.g., top_system) that has two levels, i.e., it has two instances of a subsystem (e.g., subsystem_0) which itself has four instances of another subsystem (e.g., subsystem_1). When I click Generate HDL for subsystem_0, HDL is generated successfully. But when I do the same for top_system, I face this error in the command line (and synthesis of the design fails later on because of it):

java.lang.IllegalArgumentException: subsystem_1: no such parameter: componentDefinition

And indeed in top_system.qsys file, there's no componentDefinition field for subsystem_1 instances, whereas in subsystem_0.qsys this field exists for instances of subsystem_1. What am I missing here?

Thanks in advance for your help.