RH-SSO 7.6.6 consumes 100% of the CPU when using x509 authentication

Issue

After upgrading to RH-SSO 7.6.6, my customer faces following error repeatedly. The thread was killed by TransactionReaper. It indicates the thread was stuck.

2024-02-08 14:25:01,442 WARN  [com.arjuna.ats.arjuna] (Transaction Reaper) ARJUNA012117: TransactionReaper::check processing TX 0:ffff7f000001:20e56aaa:65c4643b:84 in state  RUN
2024-02-08 14:25:01,451 WARN  [com.arjuna.ats.arjuna] (Transaction Reaper Worker 0) ARJUNA012095: Abort of action id 0:ffff7f000001:20e56aaa:65c4643b:84 invoked while multiple threads active within it.
2024-02-08 14:25:01,477 WARN  [com.arjuna.ats.arjuna] (Transaction Reaper Worker 0) ARJUNA012381: Action id 0:ffff7f000001:20e56aaa:65c4643b:84 completed with multiple threads - thread default task-2 was in progress with org.keycloak.authentication.authenticators.x509.UserIdentityExtractor$SubjectAltNameExtractor.unwrap(UserIdentityExtractor.java:210)
org.keycloak.authentication.authenticators.x509.UserIdentityExtractor$SubjectAltNameExtractor.extractUserIdentity(UserIdentityExtractor.java:175)
org.keycloak.authentication.authenticators.x509.X509ClientCertificateAuthenticator.authenticate(X509ClientCertificateAuthenticator.java:104)
org.keycloak.authentication.DefaultAuthenticationFlow.processSingleFlowExecutionModel(DefaultAuthenticationFlow.java:460)
org.keycloak.authentication.DefaultAuthenticationFlow.processFlow(DefaultAuthenticationFlow.java:286)
org.keycloak.authentication.DefaultAuthenticationFlow.processSingleFlowExecutionModel(DefaultAuthenticationFlow.java:395)
org.keycloak.authentication.DefaultAuthenticationFlow.processFlow(DefaultAuthenticationFlow.java:264)
org.keycloak.authentication.DefaultAuthenticationFlow.processSingleFlowExecutionModel(DefaultAuthenticationFlow.java:395)
org.keycloak.authentication.DefaultAuthenticationFlow.continueAuthenticationAfterSuccessfulAction(DefaultAuthenticationFlow.java:196)
org.keycloak.authentication.DefaultAuthenticationFlow.processAction(DefaultAuthenticationFlow.java:172)
org.keycloak.authentication.AuthenticationProcessor.authenticationAction(AuthenticationProcessor.java:990)
org.keycloak.services.resources.LoginActionsService.processFlow(LoginActionsService.java:314)
org.keycloak.services.resources.LoginActionsService.processAuthentication(LoginActionsService.java:285)
org.keycloak.services.resources.LoginActionsService.authenticate(LoginActionsService.java:277)
org.keycloak.services.resources.LoginActionsService.authenticateForm(LoginActionsService.java:342)