Given a quality gate including a condition of critical issues over leak period, the analyzed project reports a different number of Critical Issues on the leak period in the issues page.
It might be an Index inconsistency. You should start first rebuilding it and see how it goes:
Stop SonarQube
Delete the data/es6 directory
Restart SonarQube
Be careful, it might take time.
You might also fall into the issue described into SONAR-8425: When Leak period is a number of days, leak of issues is not correctly computed. Is your leak period defines this way?
On recent versions of SQ (8.x) this bug is no longer relevant. Though I think it is still possible on 7.9 LTS. Anyway, you should consider upgrading to one of these 2 versions (LTS or latest), 6.7 is EOL.