there is a major bug with HttpsURLConnection as it breaks
the contract of equals. So the instance cannot be contained (mostly
removed) in any collection reliably. (Concurrent)HashMap has a provision to
test equality by reference prior calling equals, though.
Finding the bug in production is quite a ride as the http variant doesn't
exhibit the problem.

Here is a simple test case.

   public static void main(String[] args) throws Throwable{
     URLConnection c = new URL("https://oracle.com").openConnection();
     System.out.println(c.getClass().getName()+" equals self: "
+c.equals(c));
     c.getInputStream().close();
     System.out.println(c.getClass().getName()+" equals self: "
+c.equals(c));
   }


The culprit is in HttpsURLConnectionImpl.equals that blindly calls
delagate.equals:

//// BUG >>>> Not comparing with the delegate
    public boolean equals(Object obj) {
        return delegate.equals(obj);
    }

It should be changed to:

    public boolean equals(Object obj) {
        return this==obj || (obj instanceof HttpsURLConnectionImpl) &&
delegate.equals( ((HttpsURLConnectionImpl)obj).delegate );
    }