The reason that you do not see any block dumps in the trace file is that you are using parallel execution, and looking at the wrong trace file. Events set in query coordinator's session, are inherited by the parallel execution slaves (as are parameter settings). So when the error was signalled in the slave session and propagated to the query coordinator, both processes would have dumped a process state. You are looking at the query coordinator's trace file. You will find the dump of the block for which the consistent read failed in the trace file of the slave process that actually got the error.
I tried to get more information on the ORA-1555 errors. I used
alter session set events '1555 trace name processstate forever, level 10';
like you indicated.
I don't see the data block dump and the RBS header block dump as you
have shown in the trace. Do I have to format the trace using some tool,
like tkprof. I am new to reading process state dumps. Is there any
reference document that describes how to read different oracle dumps.
Could you point me in the right direction. I have attached the process
state dump, in case you are interested and find something obvious.