It's particularly normal for them to find issues that were let by at a prior point, as some reviewers are more lenient than others. But once they find something

It's particularly normal for them to find issues that were let by at a prior point, as some reviewers are more lenient than others. But once they find something, you're stuck with it. If those bugfixes are important, you can also ask for them to let it through, and postpone dealing with the login issue until the next release. They'll do this for bugfix-only releases. You can also keep appealing if you believe you're right, it'll eventually escalate.