Consider code like:
---
public class Test {
    public void test(Integer i) {
        switch (i) {
            case (Integer ii): break;
        }
    }
}
---

Compiling it leads to:
---
$ javac Test.java
An exception has occurred in the compiler (17-internal). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program, the following diagnostic, and the parameters passed to the Java compiler in your report. Thank you.
java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.handleSwitch(TransPatterns.java:275)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.visitSwitch(TransPatterns.java:258)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCSwitch.accept(JCTree.java:1294)
---

The cause is that the source level/preview check is not being done on the parenthesized pattern in this case.