jshell> new Throwable()
$1 ==> java.lang.Throwable

jshell> new Throwable()
$2 ==> java.lang.Throwable

jshell> $1.initCause($2)
$3 ==> java.lang.Throwable

jshell> $2.initCause($1)
$4 ==> java.lang.Throwable

jshell> throw $1
| State engine terminated.
| Restore definitions with: /reload -restore

jshell>

---
It's likely a low-priority corner case. java.lang.ThreadGroup.uncaughtException uses Throwable.printStackTrace(System.err), which has guards against it, but JShell uses something else, that doesn't:

jshell> /reload -restore
| Restarting and restoring from previous state.
-: new Throwable()
-: new Throwable()
-: $1.initCause($2)
-: $2.initCause($1)

jshell> $1.printStackTrace()
java.lang.Throwable
at REPL.$JShell$2.do_it$($JShell$2.java:7)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
at java.base/java.lang.reflect.Method.invoke(Method.java:565)
at jdk.jshell/jdk.jshell.execution.DirectExecutionControl.invoke(DirectExecutionControl.java:227)
at jdk.jshell/jdk.jshell.execution.RemoteExecutionControl.invoke(RemoteExecutionControl.java:121)
at jdk.jshell/jdk.jshell.execution.DirectExecutionControl.invoke(DirectExecutionControl.java:125)
at jdk.jshell/jdk.jshell.execution.ExecutionControlForwarder.processCommand(ExecutionControlForwarder.java:148)
at jdk.jshell/jdk.jshell.execution.ExecutionControlForwarder.commandLoop(ExecutionControlForwarder.java:266)
at jdk.jshell/jdk.jshell.execution.Util.forwardExecutionControl(Util.java:78)
at jdk.jshell/jdk.jshell.execution.Util.forwardExecutionControlAndIO(Util.java:148)
at jdk.jshell/jdk.jshell.execution.RemoteExecutionControl.main(RemoteExecutionControl.java:74)
Caused by: java.lang.Throwable
at REPL.$JShell$3.do_it$($JShell$3.java:7)
... 10 more
Caused by: [CIRCULAR REFERENCE: java.lang.Throwable]

jshell>