As reported here:

https://mail.openjdk.java.net/pipermail/amber-spec-experts/2021-July/003049.html

Consider this case:
---
public class SwitchCoverage {
    sealed interface A {}
    sealed interface B1 extends A {}
    sealed interface B2 extends A {}
    sealed interface C extends A {}
    final class D1 implements B1, C {}
    final class D2 implements B2, C {}
    
    void test(A arg) {
        int i = switch (arg) {
            case B1 b1 -> 1;
            case B2 b2 -> 2;
        };
    }
    
}
---

The case should be considered exhaustive, but it is not.