Steps to reproduce:
1. Start JMC
2. Start a JVM listening in rjmx port 7091  in the same machine 
3. In the JVM Browser, click on the Create New Connection button in the toolbar.
4. Enter localhost as hostname and 7091 as port and press Finish.
5. In the JVM Browser, rightclick on localhost and select "Start JMX Console" in the context menu.
6. Switch to the Triggers tab.
7. In the Trigger Rules tree, select the available CPU Usage - JVM Process (Too High) rule.
8. In the Rule Details section, change Max trigger value to 0 %.
9. Click the Action sub-tab, and change the Trigger Action to "Start Continuous Flight Recording"
10. Enable the CPU Usage - JVM Process (Too High) rule by checking the checkbox next to it.
11. Click "Flight Recorder" under localhost

Actually behavior: "Flight Recorder" is not working as expected for localhost:7091 connection, refer to recorder-issue.png.

By the way,
As for JDK16 and JDK11, "Flight Recorder" is working on " org.openjdk.jmc.test.zoo.base.ZooLauncher realloc" connection as expected. ( This is the direct JVM process id discovered and displayed in JVM Browser)

as for JDK8, "Flight Recorder" is working on "localhost:7091" connection and " org.openjdk.jmc.test.zoo.base.ZooLauncher realloc" connection as expected.