It seems something is broken from Show Concurrent perspective. Open any JFR-> Event browser screen -> Verify records and click on show concurrent checkbox.

The number of records displayed in JMC 7.1.2 and JMC 8 differs. JMC 8 showing lesser number of records. 

Steps to reproduce the issue:

1. Open a JFR where there are many thread sleep events in Event Browser page.
2. 
   Select Java Thread Sleep events and check the stacktrace.
3. 
   Then select a smaller section in stacktrace view (i.e. lesser number of thread sleep) and set that as stored selection so that it starts reflecting in dropdown at top.
4. 
   Verify the number of events in event tree.. for Java Thread Sleep

5. Click on Show concurrent option at top. Verify the count..
    
   For Ex:
   Total Java Thread Sleep events are 217.. I selected a set of 17 in Stacktrace view and stored it as selection. On click on show concurrent its showing only 10 events
    
   However, JMC 7.1.2 is showing 17 following the same steps.