Thank you for your response. Here are the answers to the questions you asked.
Does it happen if you only stop and start the flow graph without actually changing any connections? Yes. It still gives the same error when only stop and start the flow graph. When I do the reconfiguration without stop and start I do not get any error. However, I do not see any reconfigured parameters applied(i.e., it still runs with the previous configuration)
Does it happen if you lock(), change, unlock() — instead of stop(), change, start()? Yes, still get the same error
Does it happen if you do some reconfiguration but less than your application actually needs — e.g. replace a block with a newly-constructed identical block (should have no effect)? Yes, even for simpler applications that use tag streams. (I have used the [stop--> change block --> start] and [lock --> change parameter --> unlock] without any error before I introduce OFDM blocks and tagged streams. I started to get the error after introducing OFDM block and tagged streams.
Herewith I have attached a flow graph where I simply try to lock the flow graph print a statement and unlock it. I still get the same error. To run please change the file name in the file source block and run the python file.
If you can help me to figure the problem I really appreciate it.