ADDITIONAL SYSTEM INFORMATION :
Same result was obtained when testing under OSX/ARM64.

A DESCRIPTION OF THE PROBLEM :
When a Java method contains a labeled if condition with an instanceof pattern matching condition and then in the body does a break using that label, the compiler doesn't complain if any successor statements dereference the pattern variable. The produced code is illegal and results in a VerifyError when executed in the JVM.

The simple example under "Source code for an executable test case results in the following error when compiled and executed:

Error: Unable to initialize main class T
Caused by: java.lang.VerifyError: Bad local variable type
Exception Details:
  Location:
    T.main([Ljava/lang/String;)V @18: aload_2
  Reason:
    Type top (current frame, locals[2]) is not assignable to reference type
  Current Frame:
    bci: @18
    flags: { }
    locals: { '[Ljava/lang/String;', 'java/lang/Object' }
    stack: { 'java/io/PrintStream' }
  Bytecode:
    0000000: 1207 4c2b c100 0999 0008 2bc0 0009 4db2
    0000010: 000b 2cb6 0011 b1
  Stackmap Table:
    append_frame(@15,Object[#2])


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and execute the example class provided in "Source code for an executable test case".

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The code should fail to compile, because when breaking out of the if body the object `o` tested with instanceof is known not to be of type String and the pattern variable `s` should therefore not be dereferencable.
ACTUAL -
The code is compiled successfully (javap output pasted below) but fails to run in the JVM.

  public static void main(java.lang.String[]);
    Code:
       0: ldc #7 // String hello
       2: astore_1
       3: aload_1
       4: instanceof #9 // class java/lang/String
       7: ifeq 15
      10: aload_1
      11: checkcast #9 // class java/lang/String
      14: astore_2
      15: getstatic #11 // Field java/lang/System.out:Ljava/io/PrintStream;
      18: aload_2
      19: invokevirtual #17 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      22: return


---------- BEGIN SOURCE ----------
class T {
    public static void main(String[] args) {
        Object o = "hello";
        X: if (!(o instanceof String s)) {
            break X;
        }
        System.out.println(s);
    }
}

---------- END SOURCE ----------

FREQUENCY : always