A DESCRIPTION OF THE PROBLEM :
There are two source files:

package p;
public class Exceptions {
    private static class E extends Exception {
        public void m() { }
    }
    public static class E1 extends E {}
    public static class E2 extends E {}
}

package q;
import p.Exceptions;
import p.Exceptions.*;
public class Test {
    public static void main(String[] args) {
        try {
            if (false) { throw new E2(); }
            throw new E1();
        } catch (E1 | E2 e) {
            e.m(); // javac 11: ...defined in an inaccessible class...
        }
    }
}

Compiling with Java 11 results in an error:

q/Test.java:12: error: E.m() is defined in an inaccessible class or interface
            e.m(); // javac 11: ...defined in an inaccessible class...
             ^
1 error

Compiling with Java 17 doesn't result in an error, but running the code results in a runtime exception:

Exception in thread "main" java.lang.IllegalAccessError: failed to access class p.Exceptions$E from class q.Test (p.Exceptions$E and q.Test are in unnamed module of loader 'app')
        at q.Test.main(Test.java:12)

The difference in behavior between Java 11 and Java 17 is probably introduced with: https://bugs.openjdk.org/browse/JDK-8264696

The bug-fix was done for: https://youtrack.jetbrains.com/issue/IDEA-297529
A similar bug was opened for ecj: https://github.com/eclipse-jdt/eclipse.jdt.core/issues/198

See also the following comments:

https://github.com/eclipse-jdt/eclipse.jdt.core/issues/198#issuecomment-1177897759
https://youtrack.jetbrains.com/issue/IDEA-297529/Wrong-compilation-error-reported-when-multi-type-catch-block-references-visible-method-from-invisible-type#focus=Comments-27-6280209.0-0

REGRESSION : Last worked in version 11

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the 2 sources from the description.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A compile error reported by the compiler.
ACTUAL -
No compile error is reported, there is a runtime exception when running the code.

---------- BEGIN SOURCE ----------
package p;
public class Exceptions {
    private static class E extends Exception {
        public void m() { }
    }
    public static class E1 extends E {}
    public static class E2 extends E {}
}

package q;
import p.Exceptions;
import p.Exceptions.*;
public class Test {
    public static void main(String[] args) {
        try {
            if (false) { throw new E2(); }
            throw new E1();
        } catch (E1 | E2 e) {
            e.m(); // javac 11: ...defined in an inaccessible class...
        }
    }
}
---------- END SOURCE ----------

FREQUENCY : always