Hierarchical blocks in a flowgraph

I have created a flowgraph which includes 2 hierarchical blocks which I created myself.

 

The entire flowgraph is a transceiver. The hierarchical blocks are a receiver and transmitter.

 

When I tested the hierarchical blocks separately, they function correctly. However, when I enable both in the top flowgraph, the flowgraph executes extremely slowly. It does not respond to clicks until perhaps as much as 30 seconds later.

 

I tried taking one of the hierarchical blocks to the most basic level possible by simply using a Null Source and Sink. I still get the hang-up.

 

Is there something I am not doing in the flowgraph to enable it to run with 2 blocks? Is there some sort of configuration I need to perform to get it to run?

 

I have looked all over forums and in the docs but can't find anything to solve my problem.

 

Thanks for any help.

 

Jim

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